'X Factor' Judges Britney Spears And Demi Lovato Prepare For Debut On Sept. 12 Premiere @8 PM ET, FOX : Celebrities : ENSTARZ

Judges from the reality series "The X Factor" (L-R) L.A. Reid, Britney Spears, Demi Lovato and Simon Cowell are pictured on a video screen via satellite from Miami, Florida, during a panel discussion at the Fox television network portion of the Television Critics Association Summer press tour in Beverly Hills, California July 23, 2012. (Photo : Reuters)

After weeks of speculation about what exactly Britney Spears would be like as a judge on "The X Factor," fans will finally get to see her for themselves Thursday.

The show's newest season premieres Sept. 12 on Fox at 8 p.m Eastern time. It will be viewers' first chance to see the mean side of Spears that Simon Cowell says came through loud and clear during auditions.

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"She's very unpredictable," Cowell told reporters during a conference call. "She has taken this very seriously and she's surprisingly quite mean."

The premiere episode was screened at Grauman's Chinese Theater in Los Angeles on Tuesday night, and the Associated Press reports Spears didn't mince her words with contestants she didn't like.

"I felt like I was listening to Alvin and the Chipmunks," she reportedly told one contestant.

When another singer insulted judge Demi Lovato, Spears said, "I want to know who let you on stage."

Cowell said Spears is very opinionated, and viewers shouldn't expect her to be all compliments like former "X Factor" judge Paula Abdul.

"In the past we've had judges that never say no. [Spears] can't say no quick enough on this show. She's quite difficult to please," Cowell said.

He added that Spears and Lovato, the show's other new judge, are like "two racehorses who are very talented but very difficult to control."

"X Factor" is also due for a new host once live episodes begin airing, and reports say reality star Khloe Kardashian is the frontrunner to join Spears and company on the show.