Calvin Harris is not too pleased with his ex-girlfriend, Taylor Swift.
Swift's rep confirmed to ET on Wednesday that the 26-year-old singer wrote Harris and Rihanna's summer hit, "This Is What You Came For," under the pseudonym Nils Sjoberg, when the two were still a couple. The song was released on April 29 and instantly climbed the charts, reaching No. 4 on the Billboard 100 and No. 1 in the Dance/Electronic category.
Almost immediately after news broke that Swift had penned the tune, Harris took to Twitter, where he initially praised his ex for her musical skills. However, his tweets quickly took a turn. "And she sings on a little bit of it too. Amazing lyric writer and she smashed it as usual," he wrote. "I wrote the music, produced the song, arranged it and cut the vocals though. And initially she wanted it kept secret, hence the pseudonym."
The 32-year-old DJ then proceeded to call out Swift -- who is currently in Australia with her new boyfriend, Tom Hiddleston -- for revealing that she wrote the song. "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," he continued. "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."
Harris even brought up Swift's alleged ongoing feud with Katy Perry. "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," he tweeted. "Please focus on the positive aspects of YOUR life because you've earned a great one."
The musician concluded his rant on a positive note, writing: "God bless everyone have a beautiful day."
Swift initially supported "This Is What You Came For" when it was released, but after her split from Harris, she reportedly felt disrespected. A source told ET that "during their relationship, Taylor wrote the song, sat down at a piano and did a demo into her iPhone."
When she sent it to Harris, he apparently loved it. "They both went into a studio and did a full demo with Taylor on vocals and Calvin doing the beat," the source added. "They both knew the song would be a hit, but Taylor wrote it for Calvin and [they] both agreed it was a bad idea to let the world know they collaborated as a couple -- it would overshadow the song."