A DECADE playing world's most famous character and a millionaire before he finished school, former child star Daniel Radcliffe could have turned into a right horror.

In fact, he's one of the coolest celebs around.

In a bustling hotel room packed with journalists, agents and public relations officers, talk has turned to a matter that's united each of these differing parties; Daniel Radcliffe is truly lovely. Fact.

Despite 14 years of global adulation, the 25-year-old Harry Potter actor has the well-deserved reputation of being the rarest of things; a former child star who is unaffected, a Hollywood actor who is unassuming, and a thoroughly well-rounded man to boot.

Polite, pleasant and engaging, one by one, this hard to please crowd head in to chat to Radcliffe about his new film, What If, and duly fall under his spell.

The offbeat romcom, Radcliffe's first, sees the actor playing heartbroken hero Wallace, who realises his feelings for new best friend Chantry, played by screenwriter and actress Zoe Kazan, run deeper.

But Chantry already has a rather nice boyfriend (Rafe Spall), and she and Wallace are reluctant to reveal their true feelings, lest they ruin their friendship and Chantry's long-term relationship.

On set, the friendship between Kazan and Radcliffe was very real, and they found ways of bonding during the skinny-dipping scene.

"Zoe wrote me a message on her nipple pasties [little stick-on covers] which said, 'Hi Dan'," he reveals, laughing. "It was a concise message.

"I tried to write, 'Hi Zoe', on my bum but I seem to remember trying to do it in a mirror. My handwriting is not great at the best of times, but trying to do it backwards on my backside wouldn't have gone well."

Perhaps writing on his derriere is a skill he's yet to master but elsewhere, Radcliffe is excelling.

Like Wallace, he holds his principles dearly and has a healthy attitude towards his ex-girlfriends.

"I've always actually been pretty good in terms of the girls I've gone out with," explains the star, who's looking handsome in a pale blue shirt, offsetting his blue eyes nicely.

"They've all been pretty great. I don't have any exes that I look back on and go, 'Oh, that person was nuts'. I've always gone out with really good people and I'm still, if not friends with, on friendly terms with all of them."

And the actor, who was born in London and worked on the BBC's adaptation of David Copperfield before becoming Harry Potter at the age of 11, is clear on his reasons for keeping things amicable.

"I find the idea that life should just be one big long string of people that you've hurt and can no longer speak to and have cut out of your life, far too painful to ever let that become a reality," he adds.

"Because that's the thing, once you've loved somebody, even if you've changed and they've changed and 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."

Working such long hours on film sets means Radcliffe, who has finished writing his first screenplay and would eventually like to direct his own film, has always found love among his fellow actors.

"If you're in a film and you're an actor, and your girlfriend is not an actor and you say, 'Right, I'm going away for four months and, no, I won't see you at all during that time', that could go down really badly," he says.

Radcliffe's in a relationship with Erin Darke; they met on the set of 2013's Kill Your Darlings and, though they had "great fun" working together, the young couple are reluctant to share screen time again.

"The reason I want to try to be as private as I can about these things 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'," Radcliffe explains.

"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."

n What If is showing at cinemas now.