Taylor Swift wrote Calvin Harris’ ‘This Is What You Came For’

Taylor Swift and Calvin Harris learned first hand that you shouldn’t mix business with pleasure.

The “Wildest Dreams” singer’s rep confirmed that she penned the hit single “This Is What You Came For” for her ex under the pseudonym Nils Sjoberg, reports People.

Early Wednesday morning, reports emerged that Swift, 26, recorded a demo of the song on piano with her phone and sent it to Harris, 32. The couple then recorded a full demo of the track, which he went on to record with Rihanna. Swift retains the publishing rights to the song.

The pair mutually agreed to keep the collaboration quiet, but Harris took that promise a little too far for Swift’s liking: On April 29, the day the song dropped, Scottish-born DJ told Ryan Seacrest, “I can’t see [a collaboration with Swift] happening.”

TMZ reports that Harris’ comments hurt Swift’s feelings, leading to the demise of their relationship — and her to full-speed-ahead new romance with Tom Hiddleston, who she met at the Met Gala a week later.