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Nobody ever said Mariah Carey would come cheap.

The Grammy Award-winning superstar, who officially signed on yesterday to be a judge on American Idol, will reportedly make a whopping $18 million for just one season, a source tells People.

"Her deal is rumored to be just under $18 million for one year with an option to renew," the source says.

Related: Confirmed -- Mariah Carey Signs On as 'Idol' Judge

The multi-million dollar figure would make her the highest paid judge on any reality show, beating both her fellow pop stars Britney Spears' reported $15 million X Factor salary, and Christina Aguilera's reported $10 million salary for a third season of The Voice.

But clearly, the American Idol team sees her as worth the investment and more.

"We are proud to have one of the world's greatest-ever female singers join our show," American Idol creator and executive producer Simon Fuller said in a statement. "Mariah defines the word 'Idol' and will inspire every singer that has the honor of performing in front of her."

Video: Howard Stern Weighs in on 'Idol' Judges' Exit

Yesterday, Carey also tweeted her own excitement at joining the hit show.

"It's gonna be so much fun working on @AmericanIdol. As a singer-songwriter, I'm excited to help find and nurture new talent. LYM! --MC," she tweeted.