No. overall No. in season Title Directed by Written by Original air date U.S. viewers (millions) 66 "Belles de Jour '' Mark Piznarski Joshua Safran & Stephanie Savage September 13, 2010 (2010 - 09 - 13) 1.83 Serena and Blair enjoy their summer vacation in Paris trying to take their minds off of home. Chuck is recovering in Prague after being found and healed by Eva, a French tourist who does not know his real identity. Meanwhile, back in New York, Eleanor helps Lily make arrangements for the Fashion 's Night Out gathering at the van der Woodsen penthouse and Dan deals with raising Georgina 's newborn son Milo, while Nate meets a potential new love interest, Juliet Sharp, whom he asks out on a date. Karlie Kloss makes a cameo appearance. Absent: Taylor Momsen as Jenny Humphrey. Title reference: The 1967 film Belle de Jour. 67 "Double Identity '' Mark Piznarski Sara Goodman & Joshua Safran September 20, 2010 (2010 - 09 - 20) 1.84 Serena and Blair run into a different Chuck in Paris, and Chuck is reluctant to return to New York with Eva. Back in New York, Juliet suggests to Nate that tricking Vanessa to be with Dan might be the right thing to remove Dan from the Dan -- Serena -- Nate love triangle. Rufus learns that Dan is not Milo 's father after he checks Georgina and Milo 's blood test. Serena convinces Blair to talk Chuck into returning to Manhattan while Dan and Nate prepare to face Serena. Absent: Taylor Momsen as Jenny Humphrey. Title reference: The 1944 film Double Indemnity. 68 "The Undergraduates '' Norman Buckley Amanda Lasher September 27, 2010 (2010 - 09 - 27) 1.78 Juliet prevents Serena from joining the Hamilton House sorority. Serena and Blair find a way to expose Juliet 's sabotaging plans. Georgina finally comes clean to Dan about Milo. Chuck is afraid of introducing Eva to Lily and Rufus, since she does not know of all the things he has done in the past. Absent: Taylor Momsen as Jenny Humphrey. Title reference: The 2008 film The Graduates. 69 "Touch of Eva '' Andrew McCarthy Leila Gerstein October 4, 2010 (2010 - 10 - 04) 2.00 Nate suspects that Juliet is keeping a big secret from him and decides to confront her. Meanwhile, Blair successfully plots to make Chuck and Eva break - up, which leads to him declaring war between them. Dan finds himself torn between his feelings for Serena and Vanessa. Absent: Taylor Momsen as Jenny Humphrey. Title reference: The 1958 film Touch of Evil. 70 5 "Goodbye, Columbia '' Jeremiah Chechik Robert Hull October 11, 2010 (2010 - 10 - 11) 1.78 Juliet sends a Gossip Girl blast that starts a very damaging rumor about Serena, saying she has an STD. Vanessa becomes worried that Dan and Serena may have slept together and turns to Juliet to help her get answers. After checking Serena 's phone, Vanessa discovers than Dan and Serena did not sleep together. Vanessa then becomes collateral damage in Juliet 's vendetta against Serena when she frames her for sending an email from Serena 's phone to her English professor offering sex for grades. Elsewhere, Chuck threatens Blair 's chances to become the new assistant to powerful businesswoman Martha (Marlyne Barrett). Absent: Taylor Momsen as Jenny Humphrey and Kelly Rutherford as Lily van der Woodsen. Title reference: The 1969 film Goodbye, Columbus. 71 6 "Easy J '' Lee Shallat - Chemel Jake Coburn October 25, 2010 (2010 - 10 - 25) 1.88 Jenny returns to New York for a job interview with Tim Gunn, while Blair puts forth her best efforts to send Little J back to Hudson. After her interview with Tim Gunn is sabotaged by Blair, Jenny reveals on Gossip Girl that she and Chuck slept together. Meanwhile, Serena learns that Colin (Sam Page) is actually her college professor, which puts their relationship in grave danger. Absent: Jessica Szohr as Vanessa Abrams. Title reference: The 2010 film Easy A. 72 7 "War at the Roses '' Joe Lazarov Jessica Queller November 1, 2010 (2010 - 11 - 01) 1.82 Blair is caught off guard at her 20th birthday party. Worried that Blair and Chuck might return to their vindictive games, Serena and Nate make the warring exes sign a peace treaty. Dan comes up with a scheme that will allow Jenny to return to the Upper East Side to celebrate Rufus and Lily 's anniversary celebration, but his plan ultimately backfires. Serena and Colin try to resist their desires for each other. Swedish singer Robyn makes a cameo performing an acoustic version of "Hang with Me '' at Blair 's birthday party celebration. Absent: Taylor Momsen as Jenny Humphrey. Title reference: The 1989 film The War of the Roses. 73 8 "Juliet Does n't Live Here Anymore '' Patrick Norris Jeanne Leitenberg November 8, 2010 (2010 - 11 - 08) 1.78 Serena continues to resist temptation with her professor Colin, while Blair tries to resist temptation with Chuck. Vanessa joins Juliet 's scheme to try to bring down Serena with photos taken of her and Colin in a romantic embrace. Nate discovers that Juliet has been lying about where she lives, and that she is poor. Dan realizes that he still has feelings for Serena. In the ending scene, Juliet makes contact with Jenny and asks for her help to take Serena down and Jenny is more than happy to help. Absent: Kelly Rutherford as Lily van der Woodsen. Title reference: The 1974 film Alice Does n't Live Here Anymore. 74 9 "The Witches of Bushwick '' Ron Fortunato Sara Goodman November 15, 2010 (2010 - 11 - 15) 1.69 Serena learns that she has until the end of Chuck 's Saints & Sinners Masquerade Ball to choose between Dan or Nate. Jenny joins forces with Juliet and Vanessa to take down Serena. Meanwhile, Blair sets her sights on becoming the new face of Anne Archibald 's Foundation for Girls, but her relationship with Chuck may be problematic. In the episode, the song "Make Me Wanna Die '' by The Pretty Reckless, which is fronted by Momsen, is heard. Title reference: The 1987 film The Witches of Eastwick. 75 10 "Gaslit '' Tate Donovan Robert Hull & Joshua Safran November 29, 2010 (2010 - 11 - 29) 1.96 Lily, Rufus, Eric, Blair, Dan, and Chuck find themselves at the hospital for an overdose from Serena. Vanessa tries to frame Jenny for Juliet 's actions, thus threatening her relationship with her family. Meanwhile, Nate attempts to help his parents put the past behind them and reconcile. After successfully clearing her agenda, Juliet makes a departure from New York City, as well as Vanessa, in fear of potential vengeance from Blair. Jenny discovers Juliet 's true intentions towards Serena and gives Blair information that will help her take down Juliet. Note: This is Taylor Momsen 's last appearance on the series until the finale, though she remains credited on all season four episodes despite being absent. Title reference: The 1944 film Gaslight. 76 11 "The Townie '' Joe Lazarov Amanda Lasher & Stephanie Savage December 6, 2010 (2010 - 12 - 06) 2.06 Blair and Dan team up with Damien to find Juliet in her Connecticut hometown through a tip from Gossip Girl. Meanwhile, Nate struggles with allowing his father back into his life when the Captain announces that his parole has been granted. Also, Rufus and Chuck learn Lily is planning to sell Bass Industries. Finally, Serena 's life at the boarding school is revealed. Absent: Jessica Szohr as Vanessa. Title reference: The 2010 film The Town. 77 12 "The Kids Are Not All Right '' Allan Kroeker KJ Steinberg January 24, 2011 (2011 - 01 - 24) 1.58 A former associate of Chuck 's father, Russell Thorpe, along with his crafty and headstrong daughter Raina, return to Manhattan with some unfinished business concerning Bass Industries. Serena and Chuck unite against Lily. Meanwhile, Blair realizes that her mother, Eleanor, may be her key to becoming a future CEO. Nate worries that his father, The Captain, is having a little too much fun after his release from prison and is not taking his parole seriously. Absent: Jessica Szohr as Vanessa. Title reference: The 1979 film The Kids Are Alright. 78 13 "Damien Darko '' Jeremiah Chechik Leila Gerstein January 31, 2011 (2011 - 01 - 31) 1.51 Blair is thrilled to get an internship at W magazine to further claw her way up the ranks to become a ruling CEO, but her excitement fades when she discovers that Dan has secured one of the coveted positions along with four other top students. Meanwhile, Chuck may have finally met his match with Russell Thorpe, and his daughter Raina, when they announce that they are planning to take over Bass Industries. Serena tries a reconciliation with Ben after his release from prison. Eric engages in suspicious behavior with Damien. Nate receives alarming news about his father 's business prospects when he learns that the Captain and Russell are working together for some nefarious purpose. Absent: Jessica Szohr as Vanessa. Title reference: The 2001 film Donnie Darko. 79 14 "Panic Roommate '' Andrew McCarthy Jake Coburn February 7, 2011 (2011 - 02 - 07) 1.62 Blair enlists Nate 's help to win over her high - strung boss, Epperly, at W magazine. Meanwhile, Damien stirs up more drama when he begins playing Eric and Serena against each other in an attempt to get back at Ben. Chuck finds himself torn between business and pleasure with Raina. English band Florence and the Machine performs an acoustic version of "Cosmic Love ''. Absent: Jessica Szohr as Vanessa. Title reference: The 2002 film Panic Room and the 2011 film The Roommate. 80 15 "It - Girl Happened One Night '' Bart Wenrich Alex McNally February 14, 2011 (2011 - 02 - 14) 1.32 As Russell Thorpe is prepared to take over Bass Industries, Chuck makes one last attempt to save his father 's company by throwing a Valentine 's Day fund raiser, and tries to cut Lily loose from his company and his life. Meanwhile, at W magazine, a difficult assignment gives Blair the opportunity for a promotion. Elsewhere, Serena struggles with her feelings for Ben against her family 's disapproval. Russell fires Nate 's father from his company as he is a conflict of interest. Absent: Jessica Szohr as Vanessa. Title reference: The 1934 film It Happened One Night. 81 16 "While You Were n't Sleeping '' Norman Buckley Sara Goodman February 21, 2011 (2011 - 02 - 21) 1.57 Eric 's 18th birthday arrives, along with a drama - filled celebration. Damien blackmails Eric with the information he knows about the affidavit Lily forged against Ben. An impatient Blair decides to speed up the timetable to jump - start her career, but ultimately stretches herself too thin. Meanwhile, Serena is forced to choose between her family and a potential romance with Ben. Chuck and Lily reconcile and team up in order to save Bass Industries from Russell Thorpe. Vanessa returns to apologize to Dan. Title reference: The 1995 film While You Were Sleeping. 82 17 "Empire of the Son '' David Warren Robert Hull February 28, 2011 (2011 - 02 - 28) 1.39 Unresolved issues between Ben and Serena come to light when his mother visits. Meanwhile, Russell puts his relationship with Raina at risk by using personal information to blackmail Lily in order to destroy Chuck 's family legacy. Russell tells Chuck a devastating secret about his father. Blair and Dan 's relationship continues to build. Nate and Raina explore their feelings for each other. Lily prepares to face legal consequences for her part in Ben 's false imprisonment. William van der Woodsen makes his return to the Upper East Side. Title reference: The 1987 film Empire of the Sun. 83 18 "The Kids Stay in the Picture '' J. Miller Tobin Jessica Queller April 18, 2011 (2011 - 04 - 18) 1.43 William, along with Lily 's mother and sister, CeCe and Carol (Sheila Kelley), come to New York to support Lily as she awaits the consequences of confessing to her crime. Carol 's daughter, Charlie (Kaylee DeFer), who has been raised away from the glamour and wealth of the Upper East Side, follows her mother to the city to meet the rest of her family. Meanwhile, Blair and Dan deal with the aftermath of their kiss as Chuck realizes that he wants to win Blair back. Title reference: The 2002 film The Kid Stays in the Picture. 84 19 "Petty in Pink '' Liz Friedlander Amanda Lasher April 25, 2011 (2011 - 04 - 25) 1.55 Serena becomes suspicious of Blair and Dan spending time together, and has Charlie spy on them to find out why. Blair is reunited with Prince Louis Grimaldi (Hugo Becker) whom she met in Paris. Meanwhile, Nate helps Raina find out what happened to her mother, while Chuck 's hopes about his legacy are crushed with the reveal of devastating information from the past. Rufus and Eric try to cheer up Lily by having Lily 's annual breast cancer awareness fundraising party be held at the penthouse. Title reference: The 1986 film Pretty in Pink. 85 20 "The Princesses and the Frog '' Andrew McCarthy Leila Gerstein May 2, 2011 (2011 - 05 - 02) 1.27 A jealous Serena attempts to use information from Blair 's past to threaten her newfound happiness with Prince Louis whose parents disapprove of Blair. After discovering a shocking secret, Nate is torn between his relationship with Raina and his friendship with Chuck. A questionable friendship arises between Charlie and Vanessa. Absent: Kelly Rutherford as Lily van der Woodsen. Title reference: The 2009 film The Princess and the Frog. 86 21 "Shattered Bass '' Allison Liddi - Brown Sara Goodman May 9, 2011 (2011 - 05 - 09) 1.20 Jack Bass returns to the Upper East Side and helps Chuck, instead of helping Raina destroy him, as he prefers to be the only one to torture his nephew. Meanwhile, Blair receives Princess Sophie 's (Joanne Whalley) approval to marry Louis, after Cyrus impresses her at a party thrown by her mother Eleanor. At Blair 's party, Serena confronts Charlie about wearing her clothes without permission, in turn causing Dan to leave with Charlie. Then, they attend a Constance Billard / St. Judes alumni event together, where they run into former Constance mean girls Isobel (Nicole Fiscella) and Kati (Nan Zhang). Chuck, Jack, and Nate discover the truth about the fire and tell Russell that if he leaves New York for good, they will keep the secret from Raina. After Raina tells Nate that she will not stop until she makes Chuck feel the pain she has, Nate tells her the truth. Thinking Chuck told her, Russell lures Blair to the rooftop of Constance. Rufus discovers that Charlie has not taken her medication and shows Serena and Vanessa. Absent: Kelly Rutherford as Lily van der Woodsen. Title reference: The 2003 film Shattered Glass. 87 22 "The Wrong Goodbye '' Patrick Norris Joshua Safran May 16, 2011 (2011 - 05 - 16) 1.36 The episode continues from the earlier events of the Constance Alumni event. Georgina Sparks, now married to a friendly but boring business intern to help raise her baby, turns up at the event looking for trouble. Serena and Vanessa reluctantly join forces to find Dan and Charlie, who does not take Dan 's rejection of her well. Blair must make a choice between the men in her life when her life is in danger by Russell. Gossip Girl author Cecily von Ziegesar makes a cameo, playing a character named Cecily, a Constance alumna. Charlie befriends Georgina, who has uncovered a secret about her. The finale ends with Blair spending the summer in Monaco with Prince Louis to plan their upcoming wedding, Serena taking on a new writing job in California, Chuck and Nate traveling the world together, Vanessa moving to Spain to go to college and selling Dan 's rough draft story of his life to a publisher, Rufus spending the summer with Lily who is still under house arrest, and Dan spending his summer in the Hamptons with Eric. Charlie returns to Miami where a shocking twist is revealed: Charlie is actually a 24 - year - old professional con artist named Ivy Dickens, who was hired by Carol Rhodes to impersonate the real Charlie. Dorota is seen throwing out the trash where a positive home pregnancy test lies with the rest of the trash. Note: Jessica Szohr 's and Connor Paolo 's last appearances until the series finale. Title reference: The 1973 film The Long Goodbye.
when does lois come to new york in gossip girl
"Petty in Pink ''