Twenty years ago the world saw the shock and grief of two boys walking behind their mother’s coffin in London. To the world, she was Princess Diana. But to those boys she was simply “Mummy”.

In a moving documentary, Diana Our Mother: Her Life and Legacy, that aired on Channel 7 on Sunday night, Prince Harry and William, Duke of Cambridge, revealed previously unseen family photos and videos to illustrate their deep loss.

Diana’s sons movingly recalled their mother’s strength.

“Even now I can feel the hugs and I miss that,” Prince Harry said. “I miss that side of family – giving you the compassion that everybody needs.”

Prince William recalled how his mother was “extremely good at showing her love and what feelings were and how important it was to feel”.

But what they remember equally is how funny she was.

“One thing I would love to ask her now, because I genuinely think she got satisfaction out of dressing me and William up in the most bizarre outfits normally matching,” Harry said.

“Looking back it makes me laugh and I think, ‘How could you do that to us?'”

Prince William is keeping her memory alive among her grandchildren with lots of photos of “Granny Diana” and stories about her life.

“She’d love the children to bits but she’d be an absolute nightmare [grandmother]. She’d come and go and she’d come in at probably at bath time, creating an absolute scene – bubbles everywhere, bathwater all over the place and then leave.”

There was also anger, all these years later.

In one heart-rending scene, William remembers his mother pleading with the press to stop hounding her and the boys during a ski trip in Austria.

“People would be utterly appalled if they knew exactly what went on,” he said.

“It was an industry that lost its way quite heavily, lost its sense of decency, lost its perspective on what was appropriate.”

What the world didn’t see at the time of Diana’s funeral was the grief of two boys, of the same age as William and Harry, a world away in war-ravaged Bosnia.

They had met Diana only two weeks before her sudden death in a car crash in Paris and she had promised them they would not be forgotten.

Diana had asked landmine activists Jerry White and Ken Rutherford to secretly take her to meet the survivors of landmines in Bosnia.

Among them was Zarko Berco, who was just 12 years old and had lost a leg.

“We were so alone and we needed help. Somehow she assured us she would help,” he said.

Malic Bredoric was 15 and he too lost a leg. Twenty years on, he wept as he remembered her for the cameras.

In a graveyard, surrounded by those who took their own lives because of the impact of war, Mr Bredoric recalled what her visit gave him.

“I was lucky I had moral support from Princess Diana. It was like a powerful wind at my back, driving me on.”

For Mr Bredoric, Diana lives on. Three weeks after she died, as a direct result of her work, an international treaty was signed banning the use of landmines.

“Today, 20 years later, there are no landmines but tragically Diana is not here,” he said. “That is her legacy.”