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've already (secretly) collaborated for a track featured in the film.

"Me and Bonnie [McKee] secretly did some background vocals on that song," Perry told the outlet, referring to Spears' hit "Ooh La La!" "So maybe listen for our voices."

The 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.

"So great to see you Smurfette Katy Perry!" Spears, 31, tweeted at Perry, 28. "Can't wait for our Vegas date…"

The "Fireworks" singer isn'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's music video.

"[They] were really, really good on set," she said, adding that her boys "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."

The former X Factor judge is currently working on her new album, tentatively due out at the end of the year.

"It's definitely in the beginning stages right now," she told Seacrest. "But I want to definitely take this album and have a new approach with it and make it a little different than anything I've ever done."