UPDATED: In his fourth year of handling envelopes for the winners of the Academy Awards, PricewaterhouseCoopers partner Brian Cullinan picked a bad time for a miscue — pulling the envelope for what was supposed to be the best picture winner from the wrong pile. 
 
 As a result, presenter Warren Beatty carried the wrong envelope Sunday night, meaning that his on-stage partner, Faye Dunaway, announced “La La Land” was the winner of the night’s top prize. “Moonlight” was actually the best picture winner. 
 
 Tim Ryan, the accounting firm’s U.S. chairman and senior partner, offered an explanation Monday of the unprecedented miscue, along with his profuse apologies to the Motion Picture Academy and to the filmmakers behind the two movies. 
 
 “We clearly made a mistake and once the mistake was made we corrected it and owned up to it,” said Ryan, attributing the foul-up to “human error.” 
 
 Ryan said he had spoken to Cullinan about the episode at length. “He feels very, very terrible and horrible. He is very upset about this mistake. And as a firm, given that he is a partner of our firm, it is also my mistake and our mistake and we all feel very bad.” 
 
 Related Trump: Oscars Best Picture Flub Occurred Because Show ‘Focused So Hard’ on Him 
 
 Cullinan was positioned stage left during the evening. His colleague, Martha Ruiz, stood in the wings, stage right, Ryan said. Each had a pile of envelopes for presenters entering from their side of the stage and then a pile of “backup” envelopes for the presenters entering from the other side of the stage at the Dolby Theatre. 
 
 Cullinan pulled the lead actress envelope that was in the “backup” pile and handed it to Beatty. “There’s a stack for the backups and the ones that are not the backups and he took from the wrong stack,” Ryan explained. 
 
 Beatty hesitated twice after opening the envelope, apparently confused when he saw both the name of lead actress winner Emma Stone and “La La Land.” Not understanding Beatty’s hesitation, Dunaway said: “You’re impossible. C’mon.” Beatty then showed her the card and Dunaway announced: “La La Land.” 
 
 Asked if Beatty and Dunaway could have recognized the error, Ryan said: “No, look, it’s our job, not theirs.” 
 
 The PwC chairman said that both Cullinan and Ruiz, who had memorized all of the winners, as per company procedure, realized instantly that an error had been made. “Martha … immediately recognized that was not who won,” Ryan said. “She opened up her backup envelope to confirm her memory.” Cullinan immediately told members of the production team of the error, Ryan said. 
 
 Procedure for such a mistake calls for the PwC employees to then take the stage, along with members of the production staff, to correct the error, Ryan said. He did not know why it took more than two minutes for the correction to be made, with “La La Land” producer Jordan Horowitz delivering the news to the world that “Moonlight” was the real best picture winner. 
 
 “This is the first time in over 80 years that there has ever been a problem and again we are very disappointed in ourselves,” Ryan said. “I have reached out to the Academy and shared with them that we take full responsibility that Brian had made the mistake and the firm takes responsibility for that.” 
 
 Ryan said he was not focused now on whether the flub would hurt the firm’s relationship with the Academy or its prospects of returning for another year of counting the ballots. “I expect us to get something like this right and our focus right now is just on making sure the academy and the rest of the folks know that and the rest will play out,” Ryan said. “We are very proud of being associated with the Academy Awards. It’s good for our brand. It’s good for our people. So while I am concerned I hope we will be judged on how quickly we reacted and owned up to the issue.” 
 
 Watch the moment unfold below: ||||| Accountant Brian Cullinan was told not to use social media during the Oscars — despite tweeting a photo of Emma Stone just moments before handing Warren Beatty and Faye Dunaway the wrong envelope for Best Picture, PEOPLE has confirmed. 
 
 In the now-deleted tweet, Cullinan – one of two accountants from PricewaterhouseCoopers who handled the Oscars balloting – shared a photo of the Best Actress winner smiling while holding her award backstage. The time stamp shows it was posted at 9:05 p.m., only minutes before the Best Picture blunder occurred. 
 
 “Brian was asked not to tweet or use social media during the show,” a source tells PEOPLE. “He was fine to tweet before he arrived at the red carpet but once he was under the auspices of the Oscar night job, that was to be his only focus.” 
 
 The source continued, “Tweeting right before the Best Picture category was announced was not something that should have happened.” 
 
 The source added that it’s unclear whether the Academy will end its 83-year relationship with the accounting firm after the mix-up. 
 
 “The Academy has launched a full-scale review of its relationship with PwC but it is very complicated,” the source said. “Vote-tallying and the Oscar night job is just one part of what PwC does with the Academy. It is too early to say how this will play out but everyone is of course taking it very very seriously.” 
 
 Christopher Polk/Getty 
 
 Cullinan has not publicly commented or posted on his Twitter account since the blunder, although his PwC partner Martha Ruiz shared a selfie from the red carpet with Cullinan and Michael Strahan after the accounting firm took responsibility for the error. 
 
 PwC, the accounting firm that counts and delivers the winning Oscars envelopes, has publicly taken the blame for the incident in which La La Land was called as the Best Picture winner over the actual honoree, Moonlight. It confirmed that Cullinan mistakenly handed the presenters the duplicate Best Actress envelope instead of the Best Picture. 
 
 Cullinan and Martha Ruiz were the representatives from PwC tasked with figuring out the Oscar winners and bringing the sealed envelopes containing the well-guarded secrets to the awards show. Two PwC staffers previously told MarketWatch that for security, there are “two briefcases, that are identical, and we have two entire sets of winning envelopes.” 
 
 During the show, the two take their places on opposite sides of the stage, handing presenters their cards (depending on which side they enter from). 
 
 On top of admitting fault in the error, PwC also said that Cullinan and Ruiz did not follow protocol for correcting the error “quickly enough.” They only appeared onstage after multiple La La Land creators gave speeches – more than two minutes after La La Land was incorrectly named the winner. 
 
 Ahead of the show, both Ruiz and Cullinan seemed assured that no mistake of that kind would be made. 
 
 Cullinan told The Huffington Post before the ceremony that if a wrong winner were to be called, “We would make sure that the correct person was known very quickly. Whether that entails stopping the show, us walking onstage, us signaling to the stage manager — that’s really a game-time decision, if something like that were to happen. ” 
 
 He added, “Again, it’s so unlikely.” ||||| Owning it. PricewaterhouseCoopers, the auditing firm that handles the Oscars votes, said that they didn’t act “quickly enough” to fix the epic Best Picture flub at the 89th annual Academy Awards on Sunday, February 26. 
 
 “PwC takes full responsibility for the series of mistakes and breaches of established protocols during last night’s Oscars,” the company wrote in a statement, released late Monday, February 27, hours after they apologized for the gaffe in another earlier statement. 
 
 According to PwC, their partner Brian Cullinan accidentally handed presenters Warren Beatty and Faye Dunaway the envelope containing the winner of Best Actress, which was La La Land’s Emma Stone. After realizing their error, Beatty, 79, explained to the audience and viewers at home, "I opened the envelope and it said, 'Emma Stone, La La Land.' That's why I took such a long look at Faye. … I wasn't trying to be funny." 
 
 Eddy Chen/ABC via Getty Images 
 
 In their statement, PwC apologized for the way they handled the situation. “Once the error occurred, protocols for correcting it were not followed through quickly enough by Mr. Cullinan or his partner,” the statement continued. 
 
 The company also expressed remorse for those roped into the snafu, including Beatty, Dunaway, 76, and host Jimmy Kimmel, as well as the casts of La La Land and Moonlight. 
 
 “We wish to extend our deepest gratitude to each of them for the graciousness they displayed during such a difficult moment,” the statement said. “For the past 83 years, the Academy has entrusted PwC with the integrity of the awards process during the ceremony, and last night we failed the Academy.” 
 
 Tim Ryan, PwC’s U.S. chairman and senior partner, addressed the drama during an interview with Variety on Monday. “We clearly made a mistake, and once the mistake was made, we corrected it and owned up to it,” he said, adding that Cullinan “feels very, very terrible and horrible” about the mix-up. 
 
 “He is very upset about this mistake,” Ryan added. “And as a firm, given that he is a partner of our firm, it is also my mistake and our mistake, and we all feel very bad.” 
 
 Want stories like these delivered straight to your inbox? Sign up now for the Us Weekly newsletter! ||||| What happened at the Oscars is unprecedented. 
 
 The night’s biggest award — Best Picture — was handed to the wrong film, presumed frontrunner La La Land, because presenters Warren Beatty and Faye Dunaway were given the wrong envelope. It bore the name of La La Land’s Emma Stone, who had won Best Actress moments before. 
 
 The three credited producers for La La Land were almost through their triumphant speeches — indeed, the third, Fred Berger, was in the middle of speaking — when producer Jordan Horowitz was forced to take the microphone and say the film had lost to Moonlight. 
 
 Report from @JeffreyLAT backstage: Mid @LaLaLand acceptance, stage hand in wings said "Oh, f-ck. Oh my God. He got the wrong envelope." — Amy Kaufman (@AmyKinLA) February 27, 2017 
 
 Essentially everybody involved appeared to believe, initially, that it was a joke, from the moment that Beatty — clearly flummoxed by having an envelope that read “Emma Stone” — tried to make sense of what had happened, only to have the crowd (and his co-presenter Dunaway) think he was unnecessarily prolonging the announcement, to the moment when Berger said, “By the way, we lost.” 
 
 PricewaterhouseCoopers, the accounting firm that counts the Oscar ballots, issued a statement taking the blame for the mix-up: 
 
 We sincerely apologize to Moonlight, La La Land, Warren Beatty, Faye Dunaway, and Oscar viewers for the error that was made during the award announcement for Best Picture. The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected. We are currently investigating how this could have happened, and deeply regret that this occurred. We appreciate the grace with which the nominees, the Academy, ABC, and Jimmy Kimmel handled the situation. 
 
 On Monday, it further clarified the situation in another statement: 
 
 PwC takes full responsibility for the series of mistakes and breaches of established protocols during last night’s Oscars. PwC Partner Brian Cullinan mistakenly handed the back-up envelope for Actress in a Leading Role instead of the envelope for Best Picture to presenters Warren Beatty and Faye Dunaway. Once the error occurred, protocols for correcting it were not followed through quickly enough by Mr. Cullinan or his partner. 
 
 Variety has much more on the mix-up. 
 
 In the moment, though, it was chaos. It’s never happened in the 89-year history of the Oscars (much less in the biggest category), and it seemingly disproved one of the longest-running Oscar urban legends. 
 
 The Oscars have a procedure for what happens if the wrong name is read — but it apparently doesn’t work that well 
 
 Only two people know the names of the Oscar winners before the envelopes are opened and read. They’re always two accountants from PricewaterhouseCoopers, the firm that tabulates Oscar votes, and they carry the results in the famed briefcases that make their way down the red carpet every year. 
 
 PWC’s methods for tabulation are said to be quite rigorous, with lots of double checks and redundancies built into their system, which is designed to make sure the right winner is placed into every envelope. But the firm’s method for correcting the situation if the wrong envelope is handed to the presenters — as apparently happened with Beatty and Dunaway — is clearly not as foolproof. 
 
 As one of those two PWC accountants explains: 
 
 I guess Warren and Leo came from opposite sides https://t.co/wOcicSEg5C pic.twitter.com/EUEf1nO2gi — Ev Williams (@ev) February 27, 2017 
 
 Essentially, the PWC accountants say that in the event of a mix-up, they would signal to a stage manager that the wrong name had been read, and the stage manager would then find a way to halt the proceedings on stage. Indeed, this bit of Oscar trivia is so popular as a “what if” that stories are written about it in the press every year — what would happen if the wrong envelope were opened, or a presenter just decided to take matters into their own hands? 
 
 “We would make sure that the correct person was known very quickly. Whether that entails stopping the show, us walking onstage, us signaling to the stage manager — that’s really a game-time decision, if something like that were to happen. Again, it’s so unlikely,” Brian Cullinan, one of the two accountants (the other is Martha Ruiz) who knew the winners for this year’s awards, told the Huffington Post mere days ago. 
 
 And, granted, the process for announcing the correct winner makes much more sense for, say, Best Actor, where only one person is taking the stage, than it does for Best Picture, where everybody involved in a film swarms to the microphone. But it’s still remarkable that La La Land had all but completed its speeches, and host Jimmy Kimmel was onstage to wrap up the evening before the announcement was made. 
 
 Think of everything that had to go wrong here: Not only did the wrong envelope have to be handed to Beatty and Dunaway, but it had to include the name of the one nominee in the Best Actress category who appeared in a film nominated for Best Picture. (Had, say, Natalie Portman won for Jackie, Beatty and Dunaway would have known immediately what had happened.) 
 
 And that Best Picture nominee was the season-long frontrunner — with 14 nominations and six other Oscars to its name from earlier in the evening. So when Beatty and Dunaway announced that it had won, no one batted an eye. 
 
 But this has never happened in the history of the Oscars. The only time that comes close was in 1964, when Sammy Davis Jr. presented the award for Adaptation or Treatment Score but was handed the envelope for Original Score. And that’s a completely different situation, because the two categories had completely different sets of nominees. 
 
 Moonlight won because it smartly ran all season long as the alternative to La La Land 
 
 With La La Land’s loss, one thing becomes clear: You don’t want to be the early Oscar frontrunner. For three years in a row, the frontrunner — Boyhood in 2015, The Revenant in 2016, and La La Land in 2017 — has lost on Oscar night. And they’ve lost in three different ways, too: Boyhood faded in the stretch. The Revenant lost in a tight three-way race (to another early frontrunner, Spotlight). And La La Land lost despite being such a big Oscar frontrunner that I said if it lost, it would be the biggest Oscar upset ever. (And it is, only made more so by the ultra-bizarre circumstances around what happened.) 
 
 Only 12 Years a Slave, which won in 2014, managed to hold on to its frontrunner status from its September 2013 debut through the February 2014 awards. And it was bolstered by the sense that both Gravity and American Hustle were nipping at its heels. (Indeed, Gravity ended up winning seven awards, including Director, but not Picture, while 12 Years a Slave won a supporting acting prize and the Adapted Screenplay award along with Picture — with the situations for both eerily mirroring the La La Land vs. Moonlight split.) 
 
 You have to go all the way back to The Artist in the Oscar season of 2011 and 2012 to find an early frontrunner that essentially cruised through the whole season with nary a speed bump or major competitor. 
 
 And the Oscars’ ranked-choice voting system means that even if you’re not the number one choice of a plurality, you can still be the number two or three choice of a lot of people and pull off the win as those voters’ number one choices drop out. (Read more about this here.) And, indeed, in every other category where Moonlight and La La Land faced off — where a simple plurality carries the day — Moonlight lost. (It lost three of those categories — Cinematography, Score, and Director — to La La Land, and both films lost Editing to Hacksaw Ridge.) 
 
 In the past, the ranked-choice system has tilted toward movies about show business, consensus choices that appealed to the entertainment industry, but in 2017 it clearly worked in Moonlight’s favor. Why? 
 
 Part of this is thanks to a very smart campaign run by the movie’s studio, A24, which essentially spent the entire awards season hanging out in the runner-up slot, never accruing enough momentum to overtake La La Land, but never fading so much that it was out of the running either. And the Academy’s moves toward developing a more diverse membership, bolstered by a large influx of nominees who don’t fit the typical “older, straight white man” Oscar voter mold, could have also worked in Moonlight’s favor. But that outreach didn’t change the makeup over the Oscar voting body overnight. Something else happened. 
 
 Talk to Oscar voters and those connected to them in the weeks leading up to the Oscars, and you heard much more passion for La La Land, but Moonlight was the only other film mentioned at all consistently as everything else faded. (Vulture’s Kyle Buchanan has also talked about this phenomenon.) It certainly didn’t hurt that Moonlight had Plan B Productions — better known as Brad Pitt’s production company — in its corner, either. (Indeed, one of Moonlight’s winners is Pitt’s producing partner Dede Gardner, also an Oscar winner for 12 Years a Slave.) 
 
 Moonlight also reflects the Academy’s acceptance of both racially diverse and LGBTQ themes — notable in the wake of two straight years without acting nominees of color and the previous most famous Oscar upset of them all, which saw the historic gay romance Brokeback Mountain bested by a largely unpredicted victory by Crash. In a way, Moonlight winning is a symbolic exemplar of the Academy tossing off both of those albatrosses, if only for a single year. 
 
 But that’s not the only explanation for Moonlight’s win. Another contributing factor, among many, may be the fact that Donald Trump is president, Hollywood hates that he’s president, and Academy members may have been looking for ways to symbolically push back against his agenda with their votes. Throughout the night, categories kept going to movies that humanized the targets of Trump’s tweets, proposed laws, and vitriol, whether it was the documentary short winner The White Helmets or the Iranian foreign film winner The Salesman. 
 
 And what better film to embrace if you want to send a message to the president — symbolically — than a beautiful, aching, artistic drama about a poor, gay black man coming of age? 
 
 Oh, right, this also vindicates Marisa Tomei 
 
 One of those weirdo bits of Oscar lore — which was even hinted at in Entertainment Weekly and the Hollywood Reporter — is that when announcing the winner of Best Supporting Actress in 1993, Jack Palance read the wrong name. 
 
 He read Marisa Tomei of My Cousin Vinny, when it should have been any of the other nominees. The best explanation — Tomei was the only American in a category full of Brits, so her upset was a victory for patriotism and country — paled in comparison to the idea of an old man just making up a winner. 
 
 PWC has always insisted this was not the case, that they would have rushed the stage if Palance had actually read the wrong name. But the urban legend persisted because, well, nothing had ever happened to disprove it. 
 
 Until now, when the biggest award of the night was announced to go to the wrong film, and everybody still watching the Oscars thought there was a different Best Picture winner for more than a minute, when the procedure asserted itself for the first time in Oscars history. 
 
 It was a hell of a way to end the evening, only made more so by the fact that it accidentally vindicates Marisa Tomei after 24 years of whispers about the invalidity of her Oscar. Good for you, Marisa! You, too, are a winner! 
 
 Update: Some wording in this piece has been changed to better reflect the confluence of events that led to Moonlight’s Best Picture win. 
 
 Update 2: We’ve added a later statement from PricewaterhouseCoopers.
– The Wall Street Journal may have figured out how exactly the biggest flub in Oscars history happened Sunday night. As the paper explains, Brian Cullinan and Martha Ruiz are the two PwC partners who stand at opposite ends of the Academy Awards stage with the envelopes containing the winners, ready to hand said envelopes to the appropriate presenters—and both hold a full set of envelopes, because they don't know for certain in advance which side of the stage presenters will walk in from. Immediately prior to the Best Picture award being presented, Ruiz had handed the Best Actress envelope to presenter Leonardo DiCaprio, who then read it onstage and presented the Oscar to Emma Stone for La La Land, sources tell the Journal. Cullinan, who still had an identical Best Actress envelope in his stack, then apparently handed that envelope instead of the Best Picture envelope to presenter Warren Beatty. About three minutes before Beatty and co-presenter Faye Dunaway walked onstage to present the Best Picture award, Cullinan tweeted a photo of Stone holding her Oscar along with the caption, "Best Actress Emma Stone backstage! #PWC." The Journal says Cullinan had tweeted other photos during the awards show, but all of them, including the photo of Stone, have since been removed from his Twitter feed. (The Journal has a screenshot of the Stone tweet.) "At the end of the day, we made a human error," the US chairman and senior partner of PwC tells USA Today. He acknowledges Cullinan handed the wrong envelope to Beatty, though no mention was made of the tweeting, which TMZ says might have "distracted" Cullinan. The senior partner also tells Variety that Cullinan "feels very, very terrible and horrible. He is very upset about this mistake. And it is also my mistake, our mistake, and we all feel very bad."