Taylor Swift's ex-boyfriend Calvin Harris spoken about the 26-year-old superstar singer in a bruising series of messages on social media, calling her out for revealing she co-wrote one of his songs while praising her songwriting ability.

Swift's writing credit on the song This Is What You Came For, which featured both Harris, 32, and 28-year-old Rihanna, had previously been concealed using the pseudonym Nils Sjöberg. That is until today, when Swift's Los Angeles based management revealed to media outlets that she had written the song's lyrics.

Harris reacted on social media by re-tweeting a link to a story with the headline "Taylor Swift wrote Calvin Harris and Rihanna's hit This Is What You Came For, rep confirms."

"And she sings on a little bit of it too," Harris added. "Amazing lyric writer and she smashed it as usual."

But the 32-year-old Scottish DJ and record producer then used his social media account to clarify some of the fine print.

"I wrote the music, produced the song, arranged it and cut the vocals though," he said. "And initially [Taylor] wanted it kept secret, hence the pseudonym."

Harris also called out Swift's motives.

"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 wrote.

"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."

Swift is currently in Australia with new boyfriend, actor Tom Hiddleston.

Intriguingly Harris added "I know ... you need someone new to try and bury like Katy etc but I'm not that guy, sorry. I won't allow it."

In that statement, Harris was referring to the very public dissolution of Swift's friendship with singer Katy Perry.

Though there are various accounts of the fall out between the pair, the rough summary is that Perry's people tried to recruit dancers from Swift's tour. In response Swift, who seems to write songs like other people leave post-it notes on the refrigerator, wrote a song titled Bad Blood, about her relationship with an unnamed female artist.

"She would come up to me at awards shows and say something and walk away, and I would think, are we friends, or did she just give me the harshest insult of my life?" Perry told Rolling Stone in 2014, without naming the artist.

The day after the interview with Rolling Stone was published, Perry tweeted: "Watch out for the Regina George in sheep's clothing." Regina George is a high school character - the ringleader of a bitchy and popular clique - played by actress Rachel McAdams, in the film Mean Girls. Perry's broadside was interpreted at the time as one aimed at Swift.

Harris finished his social media missive to Swift with this: "Please focus on the positive aspects of your life because you've earned a great one. God bless everyone have a beautiful day."

This Is What You Came For was released in April, and peaked at number four on the Billboard Hot 100.