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.

The song was penned by Bonnie McKee, who is working with Perry on her follow-up to 'Teenage Dream,' and who is making a go of it as a solo artist in her own right! And that's how Perry's voice ended up as that of a background vocalist.

"Me and Bonnie secretly did some background vocals on that song," Perry told E! at the film's premiere this weekend. "So maybe listen for our voices."

Um, you bet we will. We will tune our sonar for Perry's vox in the song!

Brit Brit and Perry met up at the premiere, both rocking blue dresses in different styles and hues. They both looked like the hot pop divas they are, though.

Britney Spears Katy Perry Smurfs 2 Premiere
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Perry wore a prim and proper Tadashi Shoji dress in a cobalt-navy shade. It got its edge from the leather skirt.

Katy Perry Tadashi Shoji Dress Smurfs 2 Premiere
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She also brought her grandmother Ann Hudson along for the ride. How CUTE! Check out Gram's kitschy shirt and her blinged out cane. We so want to hang out with that sassy dame. They don't make 'em like they used to.

Katy Perry Tadashi Shoji Dress Ann Hudson Smurfs 2 Premiere
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Perry has really nice teeth, doesn't she? She looks thrilled to be fraternizing at the film's bow.

Katy Perry Tadashi Shoji Dress Smurfs 2 Premiere
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Check her out as she hangs with Smurfette. Hey, sexy ladies!

Katy Perry Tadashi Shoji Dress Smurfette Smurfs 2 Premiere
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While Perry wore a classic, tea length frock, Brit, on the other hand, went dangerously short and tight, donning a turquoise Herve Leger bandage dress that is pretty much painted on like a second skin. She looked HAWT. It also had some black piping. The heels? Those are Saint Laurent.

Britney Spears Herve Leger Smurfs 2 Premiere
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Perry wasn't the only one to bring her family to the premiere, either. Brit Brit was on hand with her boys: Sean Preston and Jayden James. They are adorbs and have cameos in the "Ooh La La" vid.

Britney Spears Herve Leger Jayden Sean Smurfs 2 Premiere
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Brit in mommy mode -- is there anything cuter?

Britney Spears Herve Leger Jayden Sean Smurfs 2 Premiere
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Brit's kids are freakin' presh. They are going to grow up to be heartbreakers...just like mom.

Britney Spears Herve Leger Jayden Sean Smurfs 2 Premiere
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Brit also shared some pictures on her Instagram.

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