Prince Harry has a 'grumpy look' on his face in most photographs for one simple reason, a royal expert has claimed.

Ahead of the exiled Prince's 40th birthday on Sunday (September 15), royal biographer Ingrid Seward is confident that Harry is happy - despite the fact he might not look it in photos. This is down to Harry's tetchy relationship with the press, she claims.

Ingrid told the Sun's YouTube channel: "I don't think it's very plausible (that he'll get elements of his past life back). I really, truly believe Harry is happy.

"He doesn't look happy in photographs because he hates being photographed, and of course we know he's got a war with all of us media.

"So when he hears the click of the camera, he puts on that grumpy look whereas Meghan's got the perma smile.

"I do think Harry is happy and I don't think for one moment that he wants to come back here (to the UK). I think he wants to be able to visit but that depends on the security and that's another story. He's always been obsessed about the security."

Harry will spend his 40th birthday in California, and it will be markedly different than his 30th. He marked that milestone, which came less than two years before he met wife Meghan Markle, with a big party at Clarence House surrounded by friends and family.

He will likely enter his forties surrounded by new friends he has made since moving to the USA four years ago.

Ingrid said that while there's a 'tinge of sadness' none of his family will be present, it is 'admirable' that he's going down his own path.

She said: "He'll be there with a crowd of people who he's probably only known for four years maximum.

"So it's very different. But I think that's very admirable. He's moved on with his life, he hasn't just sat and moaned here."

Ingrid also said that while Harry's Invictus Games have been a resounding success, he needs another of his ventures to do likewise to back up his decision to step back as a working royal.

She added: "There's a saying if you haven't made it by the time you're 40 you're never going to make it, and of course that's not true. I think that probably in the back of Harry's mind, he thinks I've got to get on with it now.

"He has the success of the Invictus Games but we can't really name anything else. I think Harry needs to get a stronger foothold into that world that he says he wants to promote so badly."