Burn! Taylor performs the song she secretly wrote for Calvin

It's the track that sparked an epic feud between Taylor Swift and her ex, Calvin Harris.

But after being accused of trying to 'tear down' her former beau by leaking that she's the brains behind his number one hit, This Is What You Came For, the star proved she gives zero f**ks by performing it at the Formula One US Grand Prix in Del Valle, Texas, over the weekend

"As a songwriter, the most rewarding feeling in the world is writing something and having a crowd sing it back to you because you know the words," she sniped to the crowd before launching into a piano-led rendition of her ex boyfriend's song.

"I've never played this song live before, but if you know it, maybe you could sing along, and I could get to know what that feels like, to hear it sung back to me."

RELATED: Why did Taylor and Calvin really break up?
RELATED: Calvin's bestie says Taylor 'was brutal'

Burn!

Since their split in May, it's emerged that Taylor secretly came up with a few lines for the track, but used the pseudonym Nils Sjoberg on the credits.

However, when they separated, stories began to emerge in the media about Taylor's involvement, prompting Calvin to accuse his ex - who'd by then moved on with Tom Hiddleston - of leaking information to steal his thunder.

Admitting she helped him write it, he tweeted, "And she sings on a little bit of it too. Amazing lyric writer and she smashed it as usual.

"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."

Then things got even more personal, with the Scottish DJ bringing her new man and Taylor's enemy Katy Perry into the fray.

"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," he wrote.

"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 (sic)".

Calvin reportedly used Rihanna on vocals, as opposed to Taylor, because neither wanted their romance to overshadow the song.

However, Tay reportedly hit "breaking point," accusing him of being "disrespectful" by insisting he'd never work with her, whilst promoting the track they'd secretly made together.

Over to you, Calvin.

Want more celebrity, entertainment and lifestyle news? Follow Be on Facebook,Twitter, Pinterest, Tumblr and Instagram