Britney Spears + Katy Perry Collaborate on Song, Hang at ‘Smurfs 2′ Premiere [Pictures]
Britney Spears and Katy Perry are forever linked by 'The Smurfs 2' -- and not just because Brit Brit sings 'Ooh La La' (the ending credits song) and Perry voices Smurfette in the flick. Perry actually sang backup on 'Ooh La La,' too! True story.