It is five years now since the unprecedented outpouring of national grief over Princess Diana. For two young men, however, the memory of her vitality and, above all, her love, remains an ever-vital part of their daily lives.

Prince William and his young brother Prince Harry have grown up into two very different characters, with Harry by far the more adventurous.

Given that difference and the two-year age gap, which tends to yawn wide in adolescence, they might have been expected to draw apart. But that has not happened. Instead, the crushing circumstances of their mother's death in Paris drew them closer together, despite Harry's continuing insecurity over his secondary role as the "spare heir".

It is their father, the Prince of Wales, who has had the responsibilityof guiding the princes towards adulthood. He has had to deal with their problems and, when they erred - and Harry has been doing a lot of that of late - it is Charles who has had the task of urging them back into line. By all accounts he has done a good job. Even Earl Spencer, the royal family's aristocratic and outspoken critic, thinks so.

Relations between Charles and his brother- in- law have been virtually non-existent since Earl Spencer launched his stinging attack on the royals in his funeral address. Charles took his comments about the insensitivity of the royal family as a personal insult. The two do at least agree on the matter of the boys' welfare, however.

In his address, Earl Spencer promised to keep a watchful eye on their development. But, as he said recently: "That was a vow made to two boys - and they are two young men now."

And fine ones, too, in his opinion. For that, he says, a lot of the credit is due to Diana.

Despite his promise to keep a handson interest in his nephews, Earl Spencer admits that he sees very little of them and does most of his communicating by email. But as he points out: "One of Diana's greater legacies to her sons and their successors is that she has made many things more acceptable in a royal context, and shown the old guard at Buckingham Palace that in fact a lot of stuff is wanted by the people as a whole."

That has given William and Harry the freedom to develop in their own way, freedom that none of their predecessors was allowed. Instead of being hidden away, they have been allowed out to find their own way in the world - at school or university, in the clubs of the King's Road and on the polo field.

Yet, even in the rough and tumble of a polo game, Prince Harry is keenly aware of his brother's position in the royal hierarchy. They play in the Highgrove team and both are fiercely competitive. But it is noticeably Harry who makes a point of passing the ball to William and not the other way round. It is a generous gesture for Harry, who is generally regarded by the professionals as the more aggressive player.

"Harry is more of a daredevil," says John Lloyd, author of the Pimm's Book of Polo. "He's gutsier and really throws himself into the game. William is quite a shy boy by nature and gets nervous playing."

When he was younger, Harry would tease his brother, saying "If you don't want to be King, I'll be King" when William sometimes found the prospect of his destiny too overpowering.

THE tragedy of that August night five years ago, however, changed their attitude forever. The intense public examination of what, in most other circumstances, would have been purely private grief, was the hardest lesson imaginable in what it means to be royal.

The time for brotherly bickering was over. Caught in the international spotlight, they sought comfort in each other. Friends would later remark how close they had become.

By one of those ironic twists it also brought them much closer to their father. In the years leading up to his separation with Diana, Charles had become something of an absent father. This was not Charles's choice - Diana was determined to remove herself as far as possible away from the royal family and, in the process, ensured that William and Harry were less involved in the rituals of the Windsors than they had been.

She was reluctant to let them go to Sandringham or Balmoral and, as her detective Ken Wharfe recalled recently, despite a plea from the Queen for them to all go on holiday together she threatened to stop "her sons" from joining a yacht, owned by the Greek shipping billionaire John Latsis. It was an empty threat but the Princess took considerable pleasure in unsettling her husband in the only way she felt she could still hurt him.

Says a member of Charles's household: "The Prince always had a great time with his sons when they were together. The problem was they weren't together as often as he would have liked." That situation changed dramatically when Diana died.

"Overnight he was cast into the role of being a single parent. He rose to the occasion and changed into being a proper father, taking charge of everything."

That is not as suffocating or as inhibiting as it might sound. The Prince of Wales was determined that his sons should not be forced to endure the restrictions that made his own adolescence so unbearable.

In William's case, Charles's leniency appears to have paid substantial dividends. As a child, William was inclined to shy away from his destiny and avert his eyes when photographers ventured near. Although there are moments even now when he draws back, William has learned to accept the attention, thanks to Charles's relaxed approach.

William, nonetheless, does not like big crowds and goes out of his way to avoid them if he possibly can. That inherent reticence carries through into his social life. While Harry likes nothing better than joining in with

... five years on

He has made it clear that he will delay taking up his royal duties until he has at least finished university, and possibly not even then. In that, he is very much his mother's son. It was Diana who insisted that her sons should enjoy as normal a youth as possible.

NOW there is a guiding sense of responsibility, however, to the way that William conducts himself, and Prince Charles has made it his business to introduce his elder son to the finer workings of the royal family and to seek his advice and youthful opinions.

After 11 September, when the Queen and Prince Charles attended the memorial service at St Paul's, William wanted to know why he hadn't been included and was annoyed no one had told him about it. He explained to his father that he felt it was his duty to be there, as he felt his presence would have been positive. Like his late mother, he instinctively knows when he can genuinely help.

Using the guidelines taught to him by his mother, Prince William has discussed plans with his father for the future, which will make the royal family more open and responsive-than it has been in the past. The way William dresses is one minor but obvious example. Instead of being stuffed into a blazer, flannels shirts and ties - as his father was - William is much like any other young man in his taste for jeans, casual shirts and sweaters.

Harry, too, instinctively rejects the royal straitjacket. But, in his case, there is an inclination to turn the freedoms his father has allowed him into licence.

Always high-spirited, he has been increasingly eager to establish his own personality - no easy matter with a father and older brother who both will one day be King. Like many youngsters of his age he has been drawn towards activities of a kind that would concern most parents - royal or otherwise.

His antics have been well recorded. He has experimented with cannabis and, on more than one occasion, drunk so much he has been sick and abusive. Drinking to get sick is typically teenage.

The presence of a mother might have put a brake on Harry's misbehaviour but, as Diana herself once admitted: "Harry's always had a mind of his own."

Even as a youngster he was always taking the kind of risks William never did - like climbing out of his top-floor window at Kensington Palace and goading his horrified detectives to come and get him as he pelted them with snowballs.

But he is the kind of young man who has always responded better to the carrot than the stick. After he was naughty he would cuddle up to Diana and wheedle his way back into her good books. He did the same with Tiggy Legge-Bourke - now Mrs Charles Pettifer - whom Charles employed as a companion to the boys after the separation.

Diana was a possessive mother and resented Tiggy's influence over the boys but, after Diana's death, it was Tiggy who did her best to take on the maternal mantle. No one can ever take the place of a mother in a child's life, yet Tiggy at least ensured that both William and Harry had a woman whose affections and warmth they could count on - a vital ingredient in their development.

The real responsibility, however, for their upbringing now lies with Charles, and there have been times when the strain of being a single parent to two adolescent boys seemed to be getting the better of him. "I worry so much for them," he told me once.

What he was not prepared to do was compromise his own beliefs in how to bring up his children. He remained constructive and nonjudgmental when Harry confessed to his misdemeanours with drink and drugs. Instead of imposing a harsh punishment, Charles sent his wayward son on a tour of a south London rehab clinic, so he could see at first hand what alcohol and drug abuse can entail.

Charles has done his level best to give both the boys a sense of belonging, challenging them with high expectations and setting standards with clear guidance about what is expected of them. "There is no point in telling them you can't do something - you have to reason it out with them," he explained to me.

That is what he did when William, bored and lonely at St Andrews university, said he wanted to leave and go somewhere else. It was Charles who pointed out that he would saddle himself with the reputation for being a quitter. Something that no prince, especially one born to inherit the throne, would like to have attached to his name.

William listened to what his father said and was persuaded to his point of view.

SUCH an even-handed policy is very different from anything the royal family has employed before. William and Harry may still succumb to the lure of alcohol and cigarettes - or even the odd puff on a joint - but these signify monumental leaps into the adult world, and nothing Charles says is going to make any difference.

He has allowed his sons to choose their own friends - and that includes girlfriends - only too well aware of the difficulties any serious relationship with the opposite sex is going to present.

There will doubtless be other problems in the years to come, as the boys are subject to restrictions that wouldn't apply to anyone else. In the wake of heightened security around the royal family, for example, William and Harry have been banned from flying on scheduled airliners outside Britain this summer - which meant William's trip to Africa and Harry's to Spain had to be cancelled.

Most pressing of all is what careers they are to follow. William has expressed an interest in conservation, while Harry hopes to follow his brother to university and has jokingly said he would like to become a professional polo player.

The likelihood is that both will spend some time in the Army. That, too, is not the handicap it might first appear. William won the sword of honour in the cadet force at Eton, while Harry has always been attracted to military life.

What is certain is that neither will be allowed to spin off in the direction entirely of their own choosing. But then neither would want to.

It is five years since the death of Diana and, in that time, they have had to learn how to face up to the responsibility that is the counterbalance of their immense privileges and wealth.

They have their father to thank for that. And they in turn are now taking just as great a concern in his welfare as he does in theirs. After William and Harry emerged victorious from their polo game, Prince Charles said he was going to join them in the next match. With one voice the boys told him "No". He had to be careful about his back and they were not going to let him play.

Charles reluctantly took heed. He knew they were talking sense and that the advice came from two sensible young men he has done so much to mould.