Katy Perry Demo of Britney Spears' 'Passenger' Leaks Online

The song was produced by Diplo and co-written by Perry and Sia.

Turns out Katy Perry gave Britney Spears' "Passenger" a shot before it wound up on the 2013 album Britney Jean

Perry's version has now leaked online, giving a taste of what the song would have sounded like delivered by a different pop star. 

The song was produced by Diplo and co-written by Perry and Sia, but apparently they thought it would be better suited for Spears. 

Had Perry decided to keep the song for herself, the timing and style seem to suggest it would have wound up on her chart-topping "Roar" and "Dark Horse"-featuring Prism album. 

Listen to about two minutes of Perry's version here and then revisit Spears' version below.