Simon Cowell on Britney Spears, Demi Lovato: 'What was I thinking?'

Britney Spears and Demi Lovato arrived today for their first tapings of "The X Factor" in Austin, Texas, just as Simon Cowell smirks, "What was I thinking?" in a new promo for the singing competition series.

Britney Spears arrived for the first auditions for the series wearing a dress which she could have stolen off a Barbie doll's back. The hot pink mini dress featured a sheer panel through the chest, which gave a peak at the singer's cleavage.

Gary Miller/WireImage

Britney Spears was pretty in pink for the first day of audtions for "The X Factor."

"Just arrived for @TheXFactorUSA auditions -- hope everyone is ready!" Spears tweeted from the Frank Erwin Center as she signed autographs for fans. "Still waiting on @SimonCowell of course."

Lovato -- also a blonde now -- arrived in a neon yellow printer frock, topped with a leather biker jacket.

"It's my first day... woo hoo!!" she tweeted. "Back in my home state... Texas are you ready??!! :D"

Lovato might not be quite so excited after seeing Fox's first promo for the season, which was released today.

"Last fall, 'The X Factor' rocked America. Now, everything is about to change," a narrator says. "Simon [Cowell] and [fellow judge] L.A. [Reid] welcome Demi and Britney as 'X Factor' judges."

The promo ends with Cowell sitting on a couch in a posh living room, in front of a grand piano.

"What was I thinking?" Cowell says.

According to TMZ, the first day of taping is going well. Sources tell the website that Spears has been articulate and even funny in her judging, though she has disagreed often with Lovato.