It's the show everyone has been talking about. So, of course, some celebs were bound to show up when Britney Spears performed her first show of her two-year stint in Vegas.
But what do you wear to a pretty cool concert - Britney's Piece of Me show? Hmmm, it's a difficult question. Katy Perry opted for what can only be described as a fairly odd and shiny American football shirt thing. She combined her top with a tutu and some knee high socks.
After the big performance, Brits tweeted to say how amazing the show was and included a sneaky peek of one of her outfits.