Britney Spears Joining Fox's "The X Factor" (NEW YORK) - Britney Spears and Demi Lovato are joining the judging panel on "The X Factor" this fall, part of Fox's effort to boost its underperforming music competition shows. The network's executives, in presenting next season's schedule to advertisers on Monday, also promised changes for "American Idol." While "Idol" remains Fox's centerpiece, as it has been for the past decade, it has lost a quarter of its audience this year. Fox is adding two new comedies and a drama in the fall, pumping new life into "Glee" by moving it to a new night with guest stars Kate Hudson and Sarah Jessica Parker and touting a midseason drama starring Kevin Bacon as "the new "24."" The Spears announcement overshadowed the others. Despite weeks of rumors, it wasn't official until she strode onto New York's Beacon Theater stage wearing a white minidress, accompanied by show creator Simon Cowell and fellow judges Lovato and L.A. Reid. "I'm so excited about the whole experience," Spears said. It's going to be so much fun and different from anything I've ever done. I'm ready to find the true star. Lovato said she was "totally stoked" to join the cast. They replace judges Paula Abdul and Nicole Scherzinger, who were dispatched along with host Steve Jones after last fall's debut season of the competition didn't meet the creator's inflated expectations. "Not to be negative about the people leaving, but we just felt the mix could be more effective and more entertaining," said Peter Rice, entertainment chairman for the Fox Networks Group. Fox's entertainment president, Kevin Reilly, also promised work on "American Idol" next season but didn't specify anything. "This year was a bigger drop-off than we anticipated," Reilly said. He said "Idol" made no changes from the previous year and there was little "urgency to view" at the beginning of the season. He said there was still a lot of life left in the franchise. "Glee," once a sensation, saw its viewership drop by 21 percent this season. It will move to Thursday nights and a comfortable 9 p.m. Eastern time slot following "The X Factor" in the fall. Reilly said the show is "poised for a creative renaissance" and has Hudson and Parker lined up for multi-episode guest slots. Part of the reason Fox moved "Glee" is to make Tuesday a four-sitcom night, with two new shows joining "New Girl" and "Raising Hope." Mindy Kaling, actress, producer and writer for "The Office," creates and stars in "The Mindy Project," a romantic comedy about a doctor looking for love. The other new comedy, "Ben and Kate," is about a pair of odd couple siblings. "We've been building comedy momentum on Tuesday, and we finally have the shows that have exactly the tone that we are looking for," Reilly said. The fall's only new drama is "The Mob Doctor," on Monday night, about a young doctor who has to pay off her family's lifelong debt to the Chicago mob. Reilly said Bacon's hiring for the midseason drama "The Following" was the casting coup of the year. Bacon plays a former FBI agent asked to come back to work to chase a serial killer he had caught once before. The killer escaped from prison and has resumed a series of grisly murders. Another comedy focused on a family, "The Goodwin Games," is due at midseason and stars actor Scott Foley, of "Felicity" and "Grey's Anatomy." Fox's long-running drama "House" is ending its run this spring, and the network is cancelling high-profile dramas "Terra Nova" and "Alcatraz." Fox also has made changes to its long-running Saturday night lineup, where "COPS" won't return until midseason. In the fall, Fox will present live sports events such as college football, Major League baseball and NASCAR races that night.