"A little bit too raw up until this point," said Prince Harry. "It's still raw."

Two decades after Princess Diana's sudden and shocking death, her royal sons Prince William and Prince Harry are for the first time publicly sharing memories of their mother, in a new documentary, "Diana, Our Mother: Her Life and Legacy."

The princes reminisce about life with their famous mother. She may have been the most photographed woman in the world, but at home, she was just Mum, reports CBS News correspondent Liz Palmer.

In new HBO documentary the royal brothers share memories of their mother publicly for the first time, twenty years after her sudden death. HBO

"She was one of the naughtiest parents," said Prince Harry. "She would come and watch us play football and, you know, smuggle sweets into our socks."

They remember, too, how she loved to dress them up in silly costumes, and to snap family pictures.

Prince William said, "We felt, you know, incredibly loved, Harry and I. And I'm very grateful that that love still feels there."

The memories are inevitably bittersweet. The last time the princes spoke to their mother, she was in Paris, hours before she died. They were far away in Scotland with their grandmother, the Queen -- and in a hurry to go out to play.

"Harry and I were in a desperate rush to say goodbye," William says. "If I'd known what was going to happen I wouldn't have been so blasé."

Harry, who was then 12, said, "How differently the conversation would have panned out" if he'd had "the slightest inkling" it was to be their last.

Now 35 years old, William is making sure that Lady Diana is recognized as Granny Diana by his own two children. "I do regularly, putting George or Charlotte to bed, talk about her and just try and remind them that there are two grandmothers, there were two grandmothers in their lives," he said.

The princes hope to remind a new generation that their mother was more than a glamorous cover girl; she was a trailblazing celebrity activist.

"People now understand the pioneering work she did for things like HIV and AIDS, for homelessness, for the landmine campaign," said journalist Roya Nikkah, who covers the royal family. "They want to introduce her to a new audience of people who didn't know her then."

The boys who knew her best have now followed her lead to become public champions for the vulnerable -- people with mental health problems, or injured servicemen, a cause Harry spoke to CBS News' Norah O'Donnell about last year.

"I hope she'd be incredibly proud," he said. "I hope she'd be sitting up there having her little party and looking down and thinking what we have achieved -- because it's a massive team effort -- what we have achieved is absolutely brilliant."

It's been clear for some time how much the princes admired and respected their mother's public activism. But what we're now learning is how much in private they just adored her sheer playfulness.

"Diana, Our Mother: Her Life & Legacy" premieres on HBO on Monday, July 24 at 10 p.m. ET.







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