The Prince of Wales with Prince William and Prince Harry outside Westminster Abbey at the funeral of Diana. Photo / Getty

By Rebecca English

The torrent of grief at the tragic loss of Diana, Princess of Wales, was unprecedented, shaking the nation - and the monarchy - to its core.

For her devastated sons, it was a bewildering, and at times frightening, experience, as they make clear in a BBC documentary.

Speaking for the first (and, they say, last) time with heart-wrenching honesty about the dark days following Diana's death, William and Harry, who were just 15 and 12 at the time, admit they struggled to cope with the 'peculiar' public reaction and the nation's "odd" desire to see them express their emotions in public.

According to the Daily Mail, other revelations in the film Diana, 7 Days - to be shown on BBC1 on Sunday evening - include William talking about his mother's "lonely and isolated" life after her divorce.

Revealing how it was Prince Charles who broke the news of their mother's death to them at Balmoral, Harry also hints at the hitherto unexplored depths of his father's own suffering, despite his bitter divorce from Diana.

And the brothers praise their grandmother, the Queen, for doing everything within her power to protect them - even removing copies of the newspapers from the castle each day - and insisting, despite intense public pressure, that they remain in Scotland to come to terms with their loss.

This is how William and Harry reveal in their own words the aching depth of their loss and how they battled to juggle their private anguish with their duty during such an extraordinary and historic time.

THE LAST TIME THEY SPOKE TO DIANA

In August 1997 they were on holiday at Balmoral with their grandmother and had not seen their mother for almost a month. Shortly before she died, Diana rang the castle to speak to her sons. William tells the documentary: "She was away abroad.

"I remember getting a phone call at the time and you think it's just a parent ringing up to have a chat and I think both Harry and I spoke to her and said we were missing her, and we wish you were back and lots of stuff."

Harry adds: "I think it was probably about teatime for us. And I was a typical young kid running around playing games with my brother and cousins and being told 'Mummy's on the phone, mummy's on the phone' and was like, 'Right, I just really want to play'. And if I had known that was the last time I was going to speak to her the conversation would have gone in a very different direction.

"And I had to live with that for the rest of my life, knowing that I was that 12-year-old boy wanting to get off the phone and wanting to go and run around and play games rather than speak to my mum."

HOW CHARLES BROKE THE NEWS

Although both princes refused to discuss in detail the moment they were told, saying it was too personal and private to discuss, Harry does reveal it was his father who came to them to break the news.

He says: "One of the hardest things for a parent to have to do is to tell your children that your other parent has died.

"How you deal with that, I don't know. But he was there for us, he was the one out of two left. And he tried to do his best to make sure we were protected and looked after.

"He was going through the same grieving process as well."

Asked about his feelings, he adds: "Disbelief. Refuse to accept it. There was no sudden outpour of grief, of course there wasn't. I don't think anybody in that position at that age would be able to understand the concept of what it actually means going forward."

William vividly recalls how he felt.

"I remember just feeling completely numb. Disorientated, dizzy, and you feel very, very confused. And you keep asking yourself 'Why me?' all the time. What have I done? Why has this happened to us?"

PRAISE FOR THEIR GRANDMOTHER

Both are generous in their praise for the Queen, who was criticised at the time for staying at Balmoral with them and failing to make any public pronouncement on Diana's death.

It also took several days for her to agree to lower the Union flag at Buckingham Palace to half-mast as an acknowledgement of the nation's loss because, in the words, of one courtier, "she hadn't even done it for her father [George VI]".

For William and Harry, however, the Queen's presence in Scotland was invaluable.

"At the time my grandmother wanted to protect her two grandsons, and my father as well," William says.

"Our grandmother deliberately removed the newspapers so there was nothing in the house at all so we didn't know what was going on.

"And back then, obviously, there were no smartphones or anything like that so you couldn't get your news, and thankfully at the time to be honest, we had the privacy to mourn and collect our thoughts and to have that space away from everybody. We had no idea that the reaction to her death would be quite so huge.

"I think it was a very hard decision for my grandmother to make. She felt very torn between being a grandmother to William and Harry and her Queen role.

"Everyone was surprised and taken aback by the scale of what happened and the nature of how quickly it happened, plus the fact that she had been challenging the Royal Family for many years beforehand."

Harry adds: "It was a case of how do we let the boys grieve in privacy, but at the same time when is the right time for them to put on their prince hats and carry out duties to mourn not just their mother, but the Princess of Wales... and a very public audience."

HAVING TO GO TO CHURCH HOURS LATER

A few hours after being told Diana had died, William and Harry appeared in public for the first time when they went to Crathie Kirk, a local church, with the Royal Family.

Although there was huge public interest in seeing them, many reacted with horror that the princes had been put through such a public ordeal as they struggled to come to terms with their loss.

Both make no bones about the fact that this was an incredibly difficult experience for them - it was 'the last thing' he wanted to do, Harry says -although now, as adults, they acknowledge it was part of their public role.

William describes how he put his "game face on", when all he wanted to do was cry in private, as they examined some of the floral tributes left outside the gates at Balmoral.

"There were quite a few flowers there and people," he says.

"I remember looking at the flowers and the notes that were left and was very touched by it but none of it sunk in.

"All I cared about was that I had lost my mother and I didn't want to be where I was.

"When we go out and do things like that and not completely breakdown you have to put on a bit of a game face.

"You have to be quite strong about it otherwise you are a walking mess. And so Harry and I, at that age, all we understood was the duty, family point."

Harry adds: "I don't remember the service but I sure remember coming back in the car and stopping and getting out at the front gates to Balmoral.

"Looking back the last thing I wanted to do was read what other people were saying about our mother. Yes, it was amazing, it was incredibly moving to know but at that point I wasn't there, I was still in shock.

"I was wearing a tiny little strange blazer with a horrible tie, and to read other people's outpouring of grief was quite odd when you are in a position almost as if people are expecting you to grieve in public. To whose benefit would that be?

"Looking back on it I'm glad that I never cried in public because there was a fine line between work and grieving while working and grieving in private. Even if someone tried to get me to cry in public I couldn't, and probably still can't. What happened then has changed me in that sense."

THE RETURN TO LONDON

For both brothers, meeting the thousands of well-meaning members of the public mourning their mother was a difficult experience. They had returned to the London to be confronted by what "seemed like more than a hundred thousand bunches of flowers scattered from the gates at Kensington Palace".

Indeed, William goes so far as to describe the screaming, wailing and desire to touch them as "peculiar" and "unusual".

He says: "Everyone was crying and wailing and wanting to touch us. It was very peculiar but obviously very touching. Again, I was 15 and Harry was 12, nothing can really describe it. It was very unusual.

"People wanted to grab us, to touch us. They were shouting, wailing, literally wailing at us, throwing flowers and yelling and sobbing and breaking down. They were fainting and collapsing."

For Harry the moment was clearly traumatic and one that he struggles with, even now.

"People were grabbing us and pulling us into their arms and stuff. I don't blame anyone for that, of course I don't.

"But it was those moments that were quite a shocking. People were screaming, people were crying, people's hands were wet because of the tears they had just wiped away from their faces before shaking my hand.

"It was so unusual for people to see young boys like that not crying when everybody else was crying. What we were doing was being asked of us was verging on normal then, but now.... Looking at us then, we must have been in just this state of shock."

For William, it was a case of grin and bear it - anything to get through the next few days.

"We didn't really talk about it that much. It was 'Right, here we go again'.

"But walking back in behind closed doors, there was a lot of hunkering down going on, just trying to survive and get through it,' he recalls.

Later in the documentary, when referring to the tunnel of grief he faced as he walked behind his mother's coffin, William adds: "It was a very alien environment.

"I couldn't understand why everyone wanted to cry as loud as they did and show such emotion as they did when they didn't really know our mother.

"I did feel a bit protective about that at times. You didn't even know her - why and how are you so upset? Now looking back, I have learnt to understand what it was she gave the world and what she gave a lot of people. Back in the Nineties there weren't many other public figures doing what she did. She was this ray of light in a fairly grey world."

WALKING BEHIND THE COFFIN

For both William and Harry, this was, without a shadow of a doubt, the most agonising part of the day they said goodbye to their mother.

According to former prime minister Tony Blair and his then aide, Alastair Campbell, discussions about whether the children should do it went right to the wire.

Neither prince reveals who first made the suggestion and they clearly are at pains to not to apportion blame or to criticise.

But it is clear that following their mother's cortege was an experience that haunts them to this day.

"It wasn't an easy decision and it was sort of a collective family decision to do that. It was one of the hardest things I have ever done," says William.

"But we were overwhelmed by how many people turned out, I mean it was just incredible.

"It was that balance between duty and family and that was what we had to do. I think the hardest thing was that walk. It was a very long, lonely walk. But then again the balance.

"Between me being Prince William and having to do my bit versus the private William who just wanted to just go into a room and cry [having] just lost his mother."

The prince describes how he tried to hide behind his hair to shut out what he was seeing, a gesture so evocative of his mother.

"I remember just hiding behind my fringe, basically," he says.

"At the time I had a lot of hair and kept my head down a lot. I just hid behind my fringe. It was just like a tiny bit of a safety blanket.

"I know that sounds ridiculous but at the time I felt if I looked at the floor with my hair over my face no one could see me.

"It sounds ridiculous now but at the time it was important to me to get through the day."

Harry, who said earlier this year that he believed he and his brother should never have been asked to follow the coffin, appears to have adopted a more conciliatory tone.

He says: "I think it was a group decision. Before I knew it found myself in a situation with a suit on and a black tie, a white shirt, I think, and I was part of it. Generally I don't have an opinion on whether that was right or wrong. I am glad I was part of it.

"Looking back on it now I am very glad I was part of it."

His memory of the day, he says, was hearing people screaming in the crowds.

"To this day I can't remember what I was thinking. I was so focused on getting it done and doing everything that was asked of me there and then and making sure I did my mother proud."

THE FUNERAL SERVICE

Throughout the documentary, Harry refers to his determination then, and now, never to cry in public. But when Elton John performed his new version of Candle In The Wind - Goodbye England's Rose - as a tribute to his mother, he admits he almost crumbled.

"When the shutters came down and I refused to let myself down about the fact that my mother had died, there were certain things that were like someone firing an arrow straight into that barrier and the head of it getting through," Harry says. "Elton John's song was incredibly emotional.

"That was part of this whole trigger system that nearby brought me to the point of crying in public, which I am glad I didn't do."

A TRIBUTE TO DIANA

Both brothers pay an emotional tribute to their mother.

"She loved Harry and I. Even after 20 years, sitting here, I still feel that love, I still feel that warmth 20 years on, which is a huge testament to her," William says.

"She had such warmth, she wanted to make people feel special. She realised she was in a unique position and could make people smile and feel better about themselves.

"If I can be even a fraction of what she was, I will be proud and hopefully make her proud.

"There is little doubt that although she has been absent from their lives longer than she was in them, Diana is still the biggest influence on everything her sons say and do."

William concurs, saying: "When you have something so traumatic as the death of your mother when you are 15 it will either make or break you. And I wouldn't let it break me. I wanted it to make me.

"I wanted her to be proud of the person I would become and I didn't want her worried or her legacy to be [that] William and Harry were completely and utterly devastated about it."

Harry says that the best lesson he learnt from her was to "be yourself in everything you do and just give as much as you can".

"When you are that young and something like that happens to you I think it is lodged in your heart and your head and stays there for a very, very long time," he admits.

"Years after, I spent a long time of my life with my head buried in the sand thinking I don't want to be Prince Harry, I don't want this responsibility, I don't want this role. Look what's happened to my mother, why does this have to happen to me?

"Now all I want to do is fill the holes that my mother has left. That's what it is about for us.

"Making a difference and making her proud.

"She was the Princess of Wales and stood for so many things, but deep down for us she was our mother and we will miss our mother and wonder every single day what it would be like having her around."