Two interesting things for you here, both concerning the same thing.
1. Taylor Swift wrote the topliney bits of 'This Is What You Came For', the song Calvin eventually released with Rihanna. Swift's 'rep' (PR) confirmed this to People, doing so under the pseudonym Nils Sjoberg.
2. Calvin has also announced that Taylor's vocals are (somewhere) in the song.
Well that's quite interesting isn't it?
YES IT IS. IT'S BLOODY INTERESTING.