Daniel Radcliffe has revealed he has had romantic relationships with his friends.

The 25-year-old actor, who stars in off-beat rom-com What If, admitted he has often strayed beyond the friend zone, sometimes only to realise they should remain there.

"I've been friends with people and it's graduated to being a relationship, and I've been friends with people where we've kind of had a moment and went, 'Oh, this will be a terrible idea if we ever went any further with this'," he said. "I've kind of had both versions of it and I think it's a very common situation."

Dan, who is dating actress Erin Darke, whom he met on the set of 2013's Kill Your Darlings, is reluctant to be open about his girlfriend.

"The reason I want to try to be as private as I can is because she's an actress, and I knew as soon as [she] experiences any success, if she's even remotely linked to me, people will say, 'Well that only happened because of going out with him'," he explained.

"People are quick to make those judgments and I wanted to make sure they can never make them about her, because I know how hard she's worked to be where she is."

The former Harry Potter star has remained on amicable terms with his ex-girlfriends.

"I've always actually been pretty good in terms of the girls I've gone out with. I don't have any exes that I look back on and go, 'Oh, that person was nuts'," he said.

"I've always gone out with really good people and I'm still, if not friends with, on friendly terms with all of them. O nce you've loved somebody, even if... things move on, there's still a part of you that loves that person, and so it would always seem a shame to look back on them with scorn."

:: What If is in cinemas now.