He's been called the polo-playing party prince, grabbing tabloid headlines for outlandish exploits that are anything but royal. Even his mother called him the "naughty one."

But as Prince Harry stands in London's Westminster Abbey Friday beside his brother, Prince William, the eyes of the world will see a 26-year-old man who has calmed down — a bit — in recent years after carving out a role as a soldier in the British army.

He is also showing signs of the legendary compassion and innate ability to connect with people that his mother, Diana, had.

Harry is William's "best man" at his wedding to Kate Middleton, a departure from royal tradition, which usually calls those standing with a royal groom "supporters."

It's no surprise Harry will be beside his older brother.

"They're extremely close," says Ciara Hunt, an expert on the Royal Family who is covering the wedding as a special correspondent for CBC News. "They're not just brothers; they're best friends."

While there may be some nervousness from senior royals and courtiers about what the wilder of the Wales brothers will say in his wedding speech, there is also the sense the fun-loving Harry wants to bring his own special touch to the celebration.

"He wants the party to go long into the night," Hunt says of the "very sociable" Harry who has reportedly arranged for bacon sandwiches to be served to any guests still standing at 6 a.m. Saturday.

Standing up for William

Being best man won't be the first time Harry stands up for William.

Harry and William take in the England-Algeria soccer match during the 2010 World Cup in Cape Town, South Africa, June 18, 2010. The two are best friends, says royal watcher Ciara Hunt. (Carlos Barria /Reuters)

"A lot of the time that Harry got in trouble over the years, he actually was protecting William," says Hunt of the booze-filled nights at London hotspots that earned him tabloid headlines.

"William was there with him, too," she says, hastening to add "I'm not saying William was doing drugs; he wasn't."

But Harry took the flak.

"He knew the future king couldn't be seen to be doing what he was doing."

Harry's tabloid ways reached their nadir with his appearance at a costume party in a Nazi uniform — a "really big mistake, so stupid," says Hunt. He later apologized.

That Harry would protect William is in a way a turnaround of events. Years earlier, as the marriage of their parents, Prince Charles and Diana, crumbled, William kept the turmoil from his little brother.

"Harry was lucky he had an older brother to protect him," said Hunt. "He was very sheltered from a lot of the fighting that went on between Charles and Diana."

Mourning his mother

After Diana was killed in a Paris car crash in 1997, the world watched as a 12-year-old Harry marched with his brother, father, grandfather and uncle behind the cortege carrying his mother's casket to the funeral at Westminster Abbey. On top of the casket was a ring of white flowers with a simple "Mummy" printed on a card in Harry's boyish hand.

Prince Harry during his final training exercise in Cyprus in March 2006. He has grown into the role of soldier and is fiercely loyal to the job and his fellow soldiers, say observers. (Cpl. Ian Holding, U.K. Ministry of Defence/Associated Press)

Harry's life has in many ways progressed in lockstep with his brother's: their schooling following the same pattern all the way through Eton College, where he excelled in sports such as rugby but not so much in his studies.

Their roles as they grow older, however, are defined by the quirk of fate that determined the order of their birth: William is the heir; Harry is the spare.

"William has a job to do — he is going to be king," says Hunt, "But in a way, what will Harry do?"

Enter the army.

"He loves his army training," says Hunt. "He's really enjoying that."

Harry's training began in 2005 at the Royal Military Academy Sandhurst. Almost a year later, he was commissioned as an officer. He has risen in the ranks (he was recently promoted to captain and is training to be a helicopter pilot) and served, under a media blackout, for two months with other British soldiers in Afghanistan.

"For him to be able to go into Afghanistan was really one of the highlights of his career, personally and professionally, which is something William will never be able to do," says Hunt.

Harry is fundamentally devoted to serving his country, Hunt said, and is deeply loyal to his army buddies.

Third in line

Lingering in the background of everything Harry does right now, though, is the fact that he is third in line to inherit the throne, behind Charles and William.

"It's a difficult balancing act trying to find a way to carve out an independent life or legacy … that's not tied to ascending the throne," says Carolyn Harris, a PhD candidate in history at Queen's University in Kingston, Ont.

And who's to say fate can't throw a curve in the line of succession?

"Often, it's forgotten just how often it's the spare who ascends to the throne," said Harris.

Prince Harry makes a face at Mutsu, left, as Lintle grabs his chin at the Mants'ase children's home in Lesotho in southern Africa on April 24, 2006. (Reuters)

She points to Charles I, Henry VIII and Harry's own great-grandfather, George VI, as examples of royals who have assumed a throne left open by the death or abdication of an older brother.

"There's only been a few instances in British history where the Crown has actually smoothly gone from one generation to another," said Harris.

If William and Kate have children, then Harry's "dynastic significance" will decrease, giving him more freedom to pursue his military, charitable and personal interests, says Harris.

Those charitable interests include Sentebale, a charity he co-founded to support AIDS/HIV orphans in the African nation of Lesotho.

In his charitable exploits, Harry shows signs of his mother. It's not the only way Diana's spirit is reflected in her younger son.

'Personal touch'

"Everything with Harry is about the personal touch, and this is where he very much has the Diana touch, the human interest," said Hunt.

The prince has an ability to connect with people and bring them together, she says.

"Harry has the personal touch that even William is lacking. William can be good at it but Harry — it's innate."

Harry might be in a soldier's uniform when he stands with William at Westminster Abbey, but there's every chance he won't be completely reined in by the formality of the occasion.

In media interviews, he has said the best man's speech will be somewhat selective; after all, his grandmother — the Queen — will be there.

But it might include some embarrassing stories, nonetheless, and if it works out as Harry wants, maybe William will "lose a bit of hair."

Harry will laugh, and William probably will, too. Harry wouldn't have it any other way.