Britney Spears Wears Two Sexy Mini-Dresses for X Factor Presentation

Britney Spears and Simon Cowell of the Fox Show 'X Factor' appear onstage at the 2012 FOX Programming Presentation at the Beacon Theatre on May 14, 2011 in New York City. Barket/PictureGroup

It's easy to see why Simon Cowell was eager to add Britney Spears to his panel of X Factor judges.

The "Toxic" singer, 30, officially announced her participation in the show during the FOX Upfront event in New York City Monday. Spears slipped into a nude Stop Staring mini-dress (by designer Alicia Estrada) and Giuseppe Zanotti shoes to join Cowell, 52, L.A. Reid, 55, and new judge Demi Lovato, 19, on stage.

"I am so excited about this whole experience. It's going to be so much fun and so different from anything I've ever done," Spears told the crowd. "I'm ready to find the true star."

Spears — engaged to Jason Trawick, 40, since December — changed into another sexy number backstage, opting for a purple Alexander Wang mini-dress. "I couldn't be more excited to join The X Factor judging panel. I'm a huge fan of the show and now I get to be a part of the action," she told Us Weekly in a statement Monday. "Simon and L.A. better watch out!"

britney spears last night
L.A. Reid, Demi Lovato, Simon Cowell, and Britney Spears at Wollman Rink – Central Park on May 14, 2012 in New York City. Dave Kotinsky/Getty Images

Also on display: Spears' 3-carat Neil Lane engagement ring, worth an estimated $90,000!

Lovato, who recently dyed her hair blonde, turned heads in a colorful design by Falguni & Shane Peacock. "I am totally stoked to be here," she exclaimed. "I'm excited to represent my generation."

Spears and Lovato have replaced former judges Paula Abdul, 49, and Nicole Scherzinger, 33, who were fired from The X Factor in January. Ex-host Steve Jones' replacement has yet to be announced.

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