Calvin Harris confirmed that his ex-girlfriend Taylor Swift wrote his June hit with Rihanna, "This Is What You Came For," earlier today (July 13). But things took a turn for the dramatic when he went off on the "Blank Space" singer in a series of tweets shortly after -- going so far as to take a swipe at her new relationship with actor Tom Hiddleston, and reference Taylor's feud with Katy Perry.

Harris retweeted a link to a PEOPLE report saying Swift's camp confirmed she penned the song and was credited under the pseudonym Nils Sjoberg in an attempt to remain anonymous. But the story also hinted that the couple's breakup was due, in part, to comments Harris later made about whether he and Swift would ever collaborate on music together.

"You know, we haven't even spoken about it. I can't see it happening though," he told Ryan Seacrest during a promo stop for "This Is What You Came For."

The producer confirmed Swift's involvement and then gave his side of the story.

"I wrote the music, produced the song, arranged it and cut the vocals though. And initially she wanted it kept secret, hence the pseudonym," he wrote. "Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though. I figure if you're happy in your new relationship you should focus on that instead of trying to tear your ex bf down for something to do.

"I know you're off tour and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it. Please focus on the positive aspects of YOUR life because you've earned a great one."

Check out Harris' tweets below.