A Britney Spears track called "Unbroken" leaked onto the internet a few years ago. The song, which was recorded for Femme Fatale, didn't make the cut for the album, and was therefore never mastered. But even in its demo form, it's still as fierce as you'd expect a Britney song to be.
The song is an ode to a lover who's put all of Britney's pieces back together. It's kind of like a fun sequel to "Piece of Me"!