Even for celebrities, ex-boyfriends / girlfriends are tough to deal with. Ex-couple Taylor Swift and Calvin Harris are one of those pairs who are having a hard time putting their ‘ship behind them.

This morning People Magazine and TMZ learned that Taylor had secretly penned Calvin Harris and Rihanna’s summer hit “This Is What You Came For,” citing a rep for Ms. Swift. It turns out Swift has been credited on the song under a pseudonym: Nils Sjoberg. According to TMZ, “during their relationship, Taylor wrote the song, sat down at a piano and did a demo into her iPhone. She sent it to Calvin, who loved it. They both went into a studio and did a full demo with Taylor on vocals and Calvin doing the beat. They both knew the song would be a hit, but Taylor wrote it for Calvin and both agreed it was a bad idea to let the world know they collaborated as a couple … it would overshadow the song.”

So Harris did the final version with Rihanna, and the song became a major hit as soon as it dropped in late April. But problems began to arise on the day of its release, when Harris spoke with Ryan Seacrest on his radio show. “Will you do a collaboration with your girlfriend [Taylor Swift]?” Seacrest asked. “You know we haven’t even spoken about it. I can’t see it happening though.”

TMZ says Swift was not pleased with Harris’ remarks, and their source describes this incident as the “breaking point” in their relationship.

Wednesday morning, Harris went off about it on Twitter once People and TMZ reported all the details. The artist revealed that Swift sings on the song, and called her out for continuing to take swipes at him despite having new boyfriend Tom Hiddleston. Brilliantly, he tells the world that he refuses to be dragged through the dirt like Katy Perry was:

And God bless you, Calvin, for being so open on Twitter. Taylor, can we expect “Bad Blood 2” on the next album?

Update: Katy Perry has responded with a tweet of her own, depicting a very animated Hillary Clinton.