One Direction star Harry Styles has addressed mounting speculation that he is bisexual, saying that he's "pretty sure" he's not.

The 19-year-old singer, who is known for being something of a ladies' man, was recently said to be having a secret relationship with DJ Nick Grimshaw.

However, Styles dismissed the rumours and reassured his legions of female fans in a new interview with GQ Magazine.

After first insisting he "didn't even know" about the reports linking him to the openly gay BBC radio 1 DJ, the superstar said: "We're not dating, no. We're just friends."

Pressed if he was in fact bisexual, Harry insisted: "Bisexual? Me? I don't think so. I'm pretty sure I'm not."

Grimshaw previously denied the duo were an item after images of them wearing each other's clothes and frequently spending nights out together sparked rumours.

But Styles is unfazed by the gossip, which he says comes with the territory.

"Some of them are funny. Some of them are ridiculous. Some of them are annoying.

"I don't want to be one of those people that complains about the rumours. I never like it when a celebrity goes on Twitter and says, "This isn't true!" It is what it is; I tend not to do that.

"The only time it gets really annoying is that if you get into a relationship and you get into a place where you really like someone and then things are being written in the papers that affect them and how they see you. Then it can get annoying."

Styles and the rest of the One Direction boys - Niall, Louis, Zayn and Liam - each appear on one of five individual covers for September's edition of GQ.