Calvin Harris is reportedly threatened with Taylor Swift's ex, Harry Styles, that he told the One Direction hottie to stay off.

A new article from OK! Magazine claimed that being jealous is a departure from the usual level-headed Calvin Harris, but there's something about Taylor Swift's ex, Harry Styles, that made him go on the offensive.

"He's not usually the jealous type, but Taylor's history with Harry has Calvin's back up big-time, because he knows how charming Harry can be and what an impact he had on Taylor," the insider claimed.

There's also the fact that Taylor Swift revealed to Calvin Harris that she's been hooking up with the One Direction member "until recently" even if they split two years ago.

The insider added, "There's no doubt he's threatened. He's made Harry aware in no uncertain terms that he needs to stop sniffing around Taylor and to stay the f*** away."

Hollywood Life, however, said that Calvin Harris has every right to be jealous of Harry Styles because the "Summer" hitmaker was dating somebody before moving on to Taylor Swift.

As the insider explained, "Calvin and Taylor met before they hooked up, but nothing happened until he split with Aarika [Wolf]. His relationship with Aarika was actually over in late January, and he met up with Taylor in February at the BRIT Awards in London and was a single man."

Taylor Swift reportedly wrote a song about Harry Styles titled, "I Knew Your Were Trouble," from the "Red" album. Another song, "Out of the Woods" was also about Harry Styles, "with lyrical references to their December romance and snowmobile accident," said Billboard.

Calvin Harris, meanwhile, doesn't want to be the subject of girlfriend Taylor Swift's revenge songs that he allegedly made her promise not to write any songs about their relationship, said Daily Mirror.