Fox entertainment president Kevin Reilly confirms it to the press by giving her a call on his cell and putting her on speaker phone.
"I'm so excited to be joining Idol," Carey said. "I can't wait to get started in a couple months."
"Idol" remains a very popular show, albeit one that has seen steady erosion in its ratings and a graying audience that doesn't sit well with advertisers.
"Although we finished the season at the top once again, although the show is as vital as ever -- Phillip Phillips went to gold faster than any artist in the history of the show -- our ratings were down," Reilly said. "Not being the only game in town now, we need to keep things fresh. We had a dialogue with everybody on the bench. We came to a mutual decision already with Jennifer (Lopez) and Steven (Tyler). We both decided it was a time for a change."
"Once again we have the biggest names in the business, like Mariah Carey, interested in doing this job," Reilly added. "So over the next couple of weeks it's really a matter of just picking the right one that's going to be the right chemistry, making a deal and finalizing this."
Reading between the lines, it looked possible that even veteran judge Randy Jackson might not return as a judge for season 12, although Reilly didn't say that outright.
"We have so many moving parts," he said. "I don't want to talk about Randy or anyone on the bench. Randy has been working with Mariah for a long, long time and is her co-manager. Randy was very instrumental in doing this deal."