Mariah Carey Mariah Carey

It's official: Mariah Carey is American Idol's newest judge.

Kevin Reilly, Fox's president of entertainment, made the announcement Monday at Fox's Television Critics Association fall TV previews after first teasing that he could not confirm any rumors — "except for one thing." He then called Carey, whose deal closed hours ago, to speak.

Is Mariah Carey joining American Idol as a judge?

"I am so excited to be joining Idol

," Carey said. "First of all, I wanted to be here today and I wish I could be there myself to tell you. It happened really quickly. I can't wait to get started in a couple of months. ... I will see you in January."Carey's deal came about quickly and original judge Randy Jackson, Carey's longtime collaborator and co-manager, was "instrumental" in getting the deal done, Reilly said. He could not say if Jackson would return for Season 12, but confirmed that Jennifer Lopez is exiting the show along with Steven Tyler. "It's 100 percent that Jennifer won't be back to the show," he said.

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Lopez's and Tyler's exits were mutual, Reilly said, after all parties decided it was time for a change. "We went into this season, really being very transparent with everyone on the show," he said. "Although we finished the season at the top again ... our ratings were down. Not being the only game in town now, we need to keep things fresh."Here are other highlights from Reilly's panel:Glee: Reilly has read the first three scripts of Season 4 and is "very happy with how seamless" the New York-Ohio split format is. Season 4 will juggle story lines in both locations, but there is no rigid formula for every episode. "At one point, I thought we would split the season down the middle [with one half taking place in Ohio and the second half in New York]," Reilly said. "Ultimately I don't think that's the way our fans want to watch the show. It is working seamlessly back and forth. ... . I think it's really gonna be a breath of fresh air on the show."The X Factor: The show is "pretty close" to finalizing deals for the new host — which could be one or two people," Reilly said. As for new judges Britney Spears and Demi Lovato, Reilly said viewers will be surprised to see how feisty both are. "[Spears is] not afraid to lay it on the line. She's tough," he said. "I think we have a real spitfire with Demi, who literally took on Simon [Cowell] on Day 1."Fringe: Reilly hopes to exorcise the "Ghost of Comic-Con" by having ordered a fifth and final season for the sci-fi series, mostly for its devoted fan base. "Fringe has had a particular fan base. We've had a checkered history with genre at best. We're one of the only networks that have tried genre. It's done a job for us on Friday," he said. "I hope we get a little bit of cred for seeing through a show that really deserved it."Ratings crown: Fox has been the top-rated network the past eight seasons, but Reilly is realistic about its chances of losing that title next season with Idol ratings eroding. "CBS has been our main competitor. ... They have the Super Bowl. We've been neck-and-neck. ... We may not win the season this year."Emmy darlings? For the first time, there are no broadcast shows nominated for Best Drama Series this year, but Reilly, without specifically naming shows, thinks Fox could break back into the mix in 2013. "I think we have two great shots at Emmy drama nods next year," he said.