Selena Gomez Sings Britney Spears at SXSW – And Britney Responds [VIDEO]

During Selena Gomez's appearance at SXSW yesterday (March 11) to promote the upcoming film 'Spring Breakers,' she and her castmates broke into an impromptu performance of '...Baby One More Time.'

A performance, we should say, that was buzzworthy enough to get even Britney Spears' attention.

Selena and crew sang a rendition of Britney's 'Everytime' in the film. So when allegations that they lip-synced surfaced, they decided to break into song to prove their vocal prowess -- but even though it was a group effort, it was Gomez's voice that took center stage.