Mariah Carey

Will Mariah Carey be an $18 million nightmare for American idol?

The superstar singer was confirmed on Monday as the newest addition to the judging panel, following the departure of Jennifer Lopez and Steven Tyler.

However, TMZ cites a source that says if Mariah is anything like she was four years ago on the show, it may be rough going.

The report claims Carey was a "nightmare to work with" during her brief stint as a guest mentor on "American Idol" in 2008.

Sources told TMZ that Mariah -- who made her mentor cameo on "Idol" Season 7 "was incredibly late for her shoot at the Beverly Hills Hotel, not very nice at all, and ridiculously nitpicky about tiny details."

J Lo was the exact opposite, the source claimed.

Meanwhile, Lopez has credited American Idol with pushing her to "grow as an artist" after stepping down as a judge from the TV talent show.

Jennifer quit the show to return to performing but insists her two years serving as a mentor to contestants has helped her to evolve.

She tells MTV News, "Whenever it's things like that, where you're working with other people, like the audience, or even another artist, like we did with the contestants on the show, you learn, you grow. And whatever I'd tell them, it was funny, it was like telling myself. Like, 'Don't forget, when you're onstage... make sure you connect and make sure it's about the feeling.'

"Because we all get caught up, when we're the ones standing there, and everybody's watching. But it's about forgetting about that and conveying a feeling. And I always feel like whenever I was telling them this over the past two years of doing Idol, that it was helping me grow as an artist as well."

Lopez calls her American Idol stint a career highlight, but admits she is ready to step back into the spotlight as a singer.

She adds, "It was a great experience to sit there and do that for a while, and I honestly feel like it was put in my life for a reason, to be part of my journey and part of my growth, because it definitely did that. But as much as I love the show, this (singing) is what I do... And that was fun and it was great, but this is what I do."

Are you excited for Mariah to take her spot on the panel?

(Image: WENN)