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Katy Perry is revealing that she recorded background vocals on "Ooh La La," the song Britney Spears made for the "Smurfs" sequel. 

Katy is telling "E! News" that she and her longtime collaborator Bonnie McKee "secretly" recorded backing vocals on the tune, telling fans to "listen for our voices." 

The pop stars were photographed together - both dressed in blue - at the Los Angeles premiere on Saturday night. 

They expressed their mutual admiration on social media the next day.  Katy tweeted a photo of their meeting, along with an all-caps, fan girl caption.  Britney tweeted Katy back calling her "Smurfette," the character she voices in the movie - and also dropped a hint about a possible future collaboration saying, "Can't wait for our Vegas date." 

Britney is rumored to announce further details about her much-anticipated Las Vegas residency in the coming months. 

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