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Katy Perry's Demo Of Britney Spears' "Passenger" Leaks Online

Katy Perry's version of Britney Spears' song "Passenger" has now leaked online. Here is a fact though, Katy actually co-wrote the song along side 'Sia'. The song was featured on Britney's "Britney Jean" album. Before the song was set for Britney, Katy actually made a demo of the song which has leaked and you can hear below.

Who sang it better?