Mariah Carey -- Hail Caesar! Diva Signs On For Huge Vegas Payday

Move over Britney Spears, it's Mariah Carey, Bitch! The singer has officially signed on as the newest resident diva in Las Vegas ... TMZ has learned.

Caesars Palace got their wish ... we're told that Mariah snuck into Vegas last week to seal the deal. Need proof? We've got video of Carey and her entourage leaving the Palace Cheesecake Factory, escorted by security.

The superstar plans to light up the Colosseum in place of Celine Dion -- who's taking a break -- the glittery one will take the reigns until she returns late this year or early 2016.

We're told the deal is super secret but ENORMOUS. To put it in perspective Britney is raking in $475K a show ... it's unfathomable Mariah accepted less. Caesars is ready to announce concert dates any day now.

Looks like she can have her cheesecake AND eat it too.