Leaks ahead of an official release are always despicable and disrespectful to the artist and all the people involved in the creative process of a song/album, and we know that very well. 
Yet, when it’s been years since the release of a track, leakers (or whatever you like to call ’em) can turn out quite useful in unveiling trivia about how this or that song came to be. 
Thanks to this new leak, now we know that the instrumental of Britney’s and Iggy Azalea’s Pretty Girls, produced by The Invisible Men, had originally been pitched to Charli XCX who wrote and recorded a totally different tune over it, called Heart In My Pocket. 
When her version of the track got scrapped, the producers rehashed the beat for UK female group Little Mix, who in turn came up with an early demo of Pretty Girls (for their third album Get Weird), penned with songwriter Maegan Cottone. 
Since the song didn’t make it onto their LP, it ended up being submitted to Britney’s label and the rest is (sad) history.

Charli XCX - Heart In My Pocket (Demo)

There's a lot the people don't know about me that I want them to know.

zyzz is in everything and each of us 🔱

Charli XCX - Heart In My Pocket (Demo)

Mind_Controller