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"Britney Spears and Katy Perry are true blue pals! The pop songstresses were all smiles at the Smurfs 2 premiere in Westwood, Calif. on Sunday, July 28, revealing to E! News that they&amp;apos;ve already (secretly) collaborated for a track featured in the film.\r\n&amp;quot;Me and Bonnie [McKee] secretly did some background vocals on that song,&amp;quot; Perry told the outlet, referring to Spears&amp;apos; hit &amp;quot;Ooh La La!&amp;quot; &amp;quot;So maybe listen for our voices.&amp;quot;&amp;#xA0;\r\n\r\nThe superstar singers, who both wore blue for the film premiere, posed for photos together and even shared their mutual respect for one another on Twitter.\r\n&amp;quot;So great to see you Smurfette Katy Perry!&amp;quot; Spears, 31, tweeted at Perry, 28. &amp;quot;Can&amp;apos;t wait for our Vegas date&amp;#x2026;&amp;quot;\r\nThe &amp;quot;Fireworks&amp;quot; singer isn&amp;apos;t the only one who has lent her vocals to the fun track, however. Spears revealed in a June 17 interview with Ryan Seacrest that her sons Sean, 7, and Jayden, 6, were naturals on the set of filming for the song&amp;apos;s music video.\r\n\r\n&amp;quot;[They] were really, really good on set,&amp;quot; she said, adding that her boys &amp;quot;were, like, acting, and my oldest son, [Sean] was right on cue every time they would tell him to do something. Later on, I got to see what they actually did on camera and it was adorable.&amp;quot;\r\nThe former X Factor judge is currently working on her new album, tentatively due out at the end of the year.\r\n\r\n&amp;quot;It&amp;apos;s definitely in the beginning stages right now,&amp;quot; she told Seacrest. &amp;quot;But I want to definitely take this album and have a new approach with it and make it a little different than anything I&amp;apos;ve ever done.&amp;quot;"^^<http://www.w3.org/2001/XMLSchema#string>
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