The Chainsmokers' Andrew Taggart has called Halsey a "bald *****" on Twitter after she praised Lady Gaga.
He's claiming the tweet is fake though and later said his account had been hacked.
It seems like the two are no longer friends despite working together on the hit single Closer.
It started after an interview with The Chainsmokers where Andrew and production partner Alex Pall said Lady Gaga's Perfect Illusion single "sucks".
Yesterday, Gaga premiered new tune A-YO and referenced their comments in a tweet promoting the release.
The Chainsmokers responded positively to the tweet with a message reading "Respect".
So far, so nice.
Then Halsey took to Twitter to praise Gaga and say how excited she was about her new album, Joanne.
A fan then mentioned to Halsey that Gaga had "dragged" The Chainsmokers in her tweet.
Halsey said it wasn't her issue which prompted the offensive tweet from Andrew's account to arrive.
It was quickly deleted, but fans quickly questioned him over screengrabs which began to circulate.
Andrew initially said the screengrabs were fake - but a follower had made a video of them following the click through to the tweet.
He then tweeted to say he had been hacked.
However, eagle-eyed Twitter users have since pointed out that Halsey has since unfollowed Andrew on Twitter.
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Both The Chainsmokers and Halsey scored the biggest hit of their careers with this summer's Closer, which topped the charts in the UK, US and across the world.
We're thinking a follow-up collaboration currently seems unlikely.
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