This Week's Hottest Parties: Demi, Britney, and Simon Have the X Factor and More!

X Factor judges Demi Lovato, Britney Spears (in Stella McCartney), and Simon Cowell linked arms at the second season premiere of their singing competition, which debuts tonight on FOX. "So amazing to see @TheXFactorUSA episode for the 1st time tonight—wow! I think u all are in for a treat," Tweeted Spears from Grauman's Chinese Theater, where the premiere was held. Click through to see more parties pictures!

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