Princes William and Harry recall their last words with Princess Diana

(CNN)Prince William and Prince Harry have spoken of their regret at the brevity of their final phone call with their mother, Princess Diana, just hours before her 1997 death in a car crash in Paris.

In a new documentary set to release on Monday by ITV in Great Britain and HBO in the United States, Prince Harry recalls how quickly he got off the phone with his mother.

The two brothers were at Balmoral Castle in Scotland when Diana called from Paris.

"I can't necessarily remember what I said, but all I do remember is regretting for the rest of my life how short the phone call was," Harry told ITV.

Diana, Princess of Wales, on holiday with Prince Harry.

Diana, Princess of Wales, on holiday with Prince Harry.

"If I'd known that that was the last time I was going to speak to my mother, the things I would have said to her," he said. "Looking back at it now -- it's incredibly hard. I have to deal with that for the rest of my life: not knowing that it was the last time I'd speak to my mum, how differently that conversation would have panned out if I'd had even the slightest inkling that her life was going to be taken that night."

In the documentary, Prince William said he and his brother had been "running around, minding our own business, playing with our cousins and having a very good time" and were in a rush to say "goodbye, see you later, can I go off?"

"If I'd known what was going to happen I wouldn't have been quite so blasé about it," the Duke of Cambridge said. "That phone call sticks in my mind quite heavily."

'Kid through and through'

Diana, Princess of Wales, holding Prince William while pregnant with Prince Harry.

Diana, Princess of Wales, holding Prince William while pregnant with Prince Harry.

The ITV documentary, "Diana, Our Mother: Her Life and Legacy," celebrates the life and work of Diana, Princess of Wales, in the 20th year since her death, according to a press release by the network.

The Duke of Cambridge said the time felt right to talk about their mother.

"There's not many days that go by that I don't think of her. Her 20th anniversary year feels like a good time to ... remember, you know, all the good things about her and hopefully provide maybe a different side to her that others haven't seen before," he said.

Lady Diana attends the Royal Ascot horse race on June 18, 1981.

Photos: Life of Princess Diana

Lady Diana attends the Royal Ascot horse race on June 18, 1981.

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Diana and Charles were wed on July 29, 1981. The princess, clad in an Emanuel wedding dress, leaves St. Paul's Cathedral with her husband.

Photos: Life of Princess Diana

Diana and Charles were wed on July 29, 1981. The princess, clad in an Emanuel wedding dress, leaves St. Paul's Cathedral with her husband.

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Diana and Charles leave St. Mary's Hospital after the birth of their first son, Prince William, on July 22, 1982, in London.

Photos: Life of Princess Diana

Diana and Charles leave St. Mary's Hospital after the birth of their first son, Prince William, on July 22, 1982, in London.

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Prince Harry shows a bit of his personality, which doesn't appear to please his mother, on June 11, 1988, on the balcony of Buckingham Palace.

Photos: Life of Princess Diana

Prince Harry shows a bit of his personality, which doesn't appear to please his mother, on June 11, 1988, on the balcony of Buckingham Palace.

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Diana sits in front of the Taj Mahal in India in November 1992.

Photos: Life of Princess Diana

Diana sits in front of the Taj Mahal in India in November 1992.

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Diana sits on Banana Beach during a trip to the West Indies on Januray 4, 1993.

Photos: Life of Princess Diana

Diana sits on Banana Beach during a trip to the West Indies on Januray 4, 1993.

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Diana and Harry are accompanied by family friend Catherine Soames and her son Harry during a pre-Easter skiing trip in Lech, Austria, on March 24, 1994.

Photos: Life of Princess Diana

Diana and Harry are accompanied by family friend Catherine Soames and her son Harry during a pre-Easter skiing trip in Lech, Austria, on March 24, 1994.

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Diana is seen at the American Red Cross headquarters in Washington on June 17, 1997. Diana was passionately involved in the British Red Cross Landmine Campaign.

Photos: Life of Princess Diana

Diana is seen at the American Red Cross headquarters in Washington on June 17, 1997. Diana was passionately involved in the British Red Cross Landmine Campaign.

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Diana, Princess of Wales listens to children during a visit to the British international school in Jakarta, Indonesia, on November 6, 1989.

Photos: Life of Princess Diana

Diana, Princess of Wales listens to children during a visit to the British international school in Jakarta, Indonesia, on November 6, 1989.

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The future princess, Lady Diana Spencer  on her first birthday at Park House, Sandringham, on July 1, 1962.

Photos: Life of Princess Diana

The future princess, Lady Diana Spencer on her first birthday at Park House, Sandringham, on July 1, 1962.

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Diana is seen during a summer holiday in Itchenor, West Sussex, in 1971.

Photos: Life of Princess Diana

Diana is seen during a summer holiday in Itchenor, West Sussex, in 1971.

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Diana, at age 14, is "kissed" by her pony, Scuffle, in 1974.

Photos: Life of Princess Diana

Diana, at age 14, is "kissed" by her pony, Scuffle, in 1974.

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Before marrrying Prince Charles, Diana worked as a nanny. Here she is seen with two of her charges in 1980, the year before she married.

Photos: Life of Princess Diana

Before marrrying Prince Charles, Diana worked as a nanny. Here she is seen with two of her charges in 1980, the year before she married.

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Lady Diana and Prince Charles in 1980.

Photos: Life of Princess Diana

Lady Diana and Prince Charles in 1980.

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Prince Charles and Diana arrive at Goldsmith Hall in London for a charity recital in March 1981.

Photos: Life of Princess Diana

Prince Charles and Diana arrive at Goldsmith Hall in London for a charity recital in March 1981.

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Lady Diana attends the Royal Ascot horse race on June 18, 1981.

Photos: Life of Princess Diana

Lady Diana attends the Royal Ascot horse race on June 18, 1981.

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Diana and Charles were wed on July 29, 1981. The princess, clad in an Emanuel wedding dress, leaves St. Paul's Cathedral with her husband.

Photos: Life of Princess Diana

Diana and Charles were wed on July 29, 1981. The princess, clad in an Emanuel wedding dress, leaves St. Paul's Cathedral with her husband.

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Diana and Charles leave St. Mary's Hospital after the birth of their first son, Prince William, on July 22, 1982, in London.

Photos: Life of Princess Diana

Diana and Charles leave St. Mary's Hospital after the birth of their first son, Prince William, on July 22, 1982, in London.

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Prince Harry shows a bit of his personality, which doesn't appear to please his mother, on June 11, 1988, on the balcony of Buckingham Palace.

Photos: Life of Princess Diana

Prince Harry shows a bit of his personality, which doesn't appear to please his mother, on June 11, 1988, on the balcony of Buckingham Palace.

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Diana sits in front of the Taj Mahal in India in November 1992.

Photos: Life of Princess Diana

Diana sits in front of the Taj Mahal in India in November 1992.

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12 of 15

Diana sits on Banana Beach during a trip to the West Indies on Januray 4, 1993.

Photos: Life of Princess Diana

Diana sits on Banana Beach during a trip to the West Indies on Januray 4, 1993.

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Diana and Harry are accompanied by family friend Catherine Soames and her son Harry during a pre-Easter skiing trip in Lech, Austria, on March 24, 1994.

Photos: Life of Princess Diana

Diana and Harry are accompanied by family friend Catherine Soames and her son Harry during a pre-Easter skiing trip in Lech, Austria, on March 24, 1994.

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Diana is seen at the American Red Cross headquarters in Washington on June 17, 1997. Diana was passionately involved in the British Red Cross Landmine Campaign.

Photos: Life of Princess Diana

Diana is seen at the American Red Cross headquarters in Washington on June 17, 1997. Diana was passionately involved in the British Red Cross Landmine Campaign.

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Diana, Princess of Wales listens to children during a visit to the British international school in Jakarta, Indonesia, on November 6, 1989.

Photos: Life of Princess Diana

Diana, Princess of Wales listens to children during a visit to the British international school in Jakarta, Indonesia, on November 6, 1989.

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The future princess, Lady Diana Spencer  on her first birthday at Park House, Sandringham, on July 1, 1962.

Photos: Life of Princess Diana

The future princess, Lady Diana Spencer on her first birthday at Park House, Sandringham, on July 1, 1962.

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Diana is seen during a summer holiday in Itchenor, West Sussex, in 1971.

Photos: Life of Princess Diana

Diana is seen during a summer holiday in Itchenor, West Sussex, in 1971.

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Diana, at age 14, is "kissed" by her pony, Scuffle, in 1974.

Photos: Life of Princess Diana

Diana, at age 14, is "kissed" by her pony, Scuffle, in 1974.

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Before marrrying Prince Charles, Diana worked as a nanny. Here she is seen with two of her charges in 1980, the year before she married.

Photos: Life of Princess Diana

Before marrrying Prince Charles, Diana worked as a nanny. Here she is seen with two of her charges in 1980, the year before she married.

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Lady Diana and Prince Charles in 1980.

Photos: Life of Princess Diana

Lady Diana and Prince Charles in 1980.

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Prince Charles and Diana arrive at Goldsmith Hall in London for a charity recital in March 1981.

Photos: Life of Princess Diana

Prince Charles and Diana arrive at Goldsmith Hall in London for a charity recital in March 1981.

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Lady Diana attends the Royal Ascot horse race on June 18, 1981.

Photos: Life of Princess Diana

Lady Diana attends the Royal Ascot horse race on June 18, 1981.

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While looking through an old photo album during the documentary, the princes recall some of the most joyful moments from their childhood. Prince Harry said Diana was a "kid through and through."

"When everybody says to me, you know, so she was fun, give us an example ... all I can hear is her laugh in my head. And that sort of crazy laugh of where there was just pure happiness shown on her face."

The brothers told the documentary makers that their mother made them feel loved.

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

His brother added: "It was that love that -- that even if she was on the other side of a room ... that you, as a son, you could feel it."

Princes William and Harry said their last conversation with their mother, Princess Diana, had been brief.

Princes William and Harry said their last conversation with their mother, Princess Diana, had been brief.

Prince William also shared a story about when Diana surprised him with a meeting with his favorite supermodels.

She had arranged "when I came home from school to have Cindy Crawford, Christy Turlington and Naomi Campbell waiting at the top of the stairs," Prince William said.

"I was probably 12 or 13-year-old boy who had posters of them on his wall. And I went bright red and didn't quite know what to say and sort of fumbled, and I think I pretty much fell down the stairs on the way up."

"Diana, Our Mother: Her Life and Legacy" will air Monday at 9 p.m. on ITV in the UK and at 10 p.m. ET on HBO in the US.

News Courtesy: www.cnn.com