Mariah Carey -- Hangs with 'X Factor' Rival Before Scoring 'American Idol' Gig

Just a day or so before being named the newest "American Idol" judge, Mariah Carey was hanging out with some of her biggest competition ... "X Factor" judge L.A. Reid.

Mimi and L.A. were spotted cruising around the Hamptons together this weekend and sources tell us he was key in convincing her to take the "Idol" gig.

Although they are now on rival TV shows, the music heavyweights go way back as Reid used to be the CEO of Mariah's record label.