A song produced by Calvin Harris and featuring the dulcet tones of 'Gentleman' denier Tinashe has surfaced online.
It's called '5AM' and sounds an awful lot like this (via Ultimate Music):
There's speculation this could have been the song Calvin was chatting about late last year that was intended for Rihanna but basically she wasn't feeling it.
It definitely sounds like Rihanna could have done it.