Mariah Carey performed a medley of her hit songs at the American Idol finale last night but her performance caused a Twitter uproar as fans discussed their disappointment with her act.

Carey sang a medley of "Vision of Love," "Make It Happen," "My All," "Hero,"
"We Belong Together" and her new single "Beautiful."

Her highly anticipated performance on a singing reality show where lip-synching is not allowed, was slammed by critics on the social media network, as they accused her of doing just that.

"Mariah Carey was either lip syncing like a mofo or my tv is delayed... I'm betting on lip synching. #AmericanIdolFinale", one user tweeted.

"Waited the entire season for @MariahCarey to perform and she gives us recorded watered down lip syncing.... she should be ashamed! #idol."

However, the chart topper denied that she lip synched, with her rep telling Entertainment Tonight: "No, she did not lip-sync! She sang 3x and even sang additional songs for fans in between [commercials.]"

Carey was not the only American Idol to sing on last night's finale. Judge Keith Urban and Randy Jackson took to the stage with Idol runner-up Kree Harrison with Urban's hit song "Where the Blacktop Ends." He also performed his single "Little Bit of Everything."

Former American Idol judge Jennifer Lopez also gave a stunning performance on the finale show. Other featured performances included Psy's new single "Gentlemen", Jennifer Hudson's duet with American Idol winner Candice Glover for "Inseparable", and Angie Miller's surprise duet with British singer Jessie J.