Britney Spears, Katy Perry

Michael Buckner/Getty Images for SONY

Who knew Britney Spears and Katy Perry have made music together?

It turns out Perry actually sings on Spears' Smurfs 2 song "Ooh La La!," the "Firework" singer exclusively reveals to E! News.

The catchy pop tune, written by frequent Perry collaborator Bonnie McKee, is played over the end credits of the Smurfs 2 movie.

"Me and Bonnie secretly did some background vocals on that song," Perry told me at today's LA premiere of the flick. "So maybe listen for our voices."

Fingers crossed Perry and Brit will do a real duet together soon.

"I can't wait to meet her," Perry said.

Spears was at the premiere rocking a blue dress, with her sons Jaden and Sean in tow.

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