The Scottish DJ didn't told back on Twitter after reading an article in which Taylor's rep confirmed: "Taylor Swift wrote 'This Is What You Came For' under the pseudonym Nils Sjoberg."
Calvin complimented his ex on her song writing skills but also criticised her decision to go public with that information when she initially wanted it kept private.
He also referenced her romance with Tom Hiddleston, which began just two weeks after her split from Calvin was confirmed.
And he threw in a Katy Perry namecheck, following all those rumours of a feud between Katy and Taylor after the former was accused of "sabotaging" a Taylor tour by hiring staff from under her.
"She sings on a little bit of it too Amazing lyric writer and she smashed it as usual.
"I wrote the music, produced the song, arranged it and cut the vocals though. And initially she wanted it kept secret, hence the pseudonym.
"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.
"God bless everyone have a beautiful day."
Er, over to you Taylor...
Pictures of Taylor and actor Tom kissing emerged just two weeks after her split from Calvin was confirmed. She'd dated Calvin for 15 months.
At the time, there were numerous reports about why Taylor and Calvin had split including allegations he didn't like being in her shadow, he didn't want marriage, he didn't like the limelight, their romance turned to friendship etc. etc.
But Calvin tweeted: "The only truth here is that a relationship came to an end and what remains is a huge amount of love and respect."
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