Zayn Malik, Louis Tomlinson and Naughty Boy are having a row on Twitter.
It seemed to start when Naughty Boy posted a picture of himself and Zayn along with the caption, "Replace this" - which Zayn then retweeted.
Louis then wrote: "Remember when you were 12 and you used to think those Mac filters for your pictures were cool haha ! Some people still do HA!"
Zayn then replied directly to Louis, saying: "Remember when you had a life..?"
Naughty Boy, who has been working with Zayn, also had his own back-and-forth row with Louis on the social network.
Naughty Boy then retweeted a more cryptic post made by Emeli Sande.
But after a few hours things seemed to calm down... a bit.
Naughty Boy is said to be working on new material with Zayn, who quit One Direction in March.
The music producer has already upset One Direction fans, by sharing a video online which seemed to suggest that he had "saved" Zayn from the band.
Louis accused Naughty Boy of being "inconsiderate" to fans after he posted the link.
A song featuring Zayn without the rest of One Direction was also taken down, less than a day after it was shared on Soundcloud.
Naughty Boy tweeted a link to the track, with the words "let the music do the talking" - less than a week after Zayn revealed he was leaving One Direction.