Prince William and Prince Harry revealed intimate memories of their late mother in a 2017 documentary

On the 23rd anniversary of Princess Diana‘s death on August 31, here’s a look back at Prince William and Prince Harry‘s decision to share intimate details of their last conversation with their mother.

The deeply personal memories were part of ITV and HBO’s Our Mother Diana: Her Life and Legacy special, which aired in 2017 to mark the 20th anniversary of Diana’s death in a Paris car crash. Princess Diana died in the early morning hours of August 31, 1997.

The princes, who said that they will not speak out at length about her like this again, spoke movingly about the fact that their last phone call from her – on the day she died – was so short. Being such young boys, aged 15 and 12 respectively, they were keen to get back to playing with their cousins at the Queen’s Scottish retreat, Balmoral.

“If I’d known that that was the last time I was going to speak to my mother the things that I would – the things I would have said to her,” Harry says in the documentary.

Diana And Harry Vj Day
Princess Diana and Prince Harry
| Credit: Tim Graham/Getty
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Princess Diana, Prince William and Prince Harry
| Credit: A.G. Carrick/Diana Memorial Fund/Getty

While discussing the documentary with reporters — including PEOPLE — at a meeting in Kensington Palace in 2017, William said, “This is a tribute from her sons to her.” He added that standing before a group about to watch the documentary was “possibly the most nervous I’ve ever been.”

“It’s one thing doing a documentary like this and it’s another thing standing front of all of you guys and explaining about something very personal to you,” he added. “Nevertheless, I think it’s very important that I’m here to do that.”

And William — who like Harry finds talking about his mother so intensely and publicly difficult — vowed, “We won’t speak as openly and as publicly about her again.”

Prince William and Princess Diana in a photo from the princes’ personal collection
| Credit: The Duke of Cambridge and Prince Harry/PA
Prince Harry and Princess Diana in a photo from the princes’ personal collection
| Credit: The Duke of Cambridge and Prince Harry/PA

William added, “We feel hopefully this film will provide the other side from her close family friends that you might not have heard from before, from those who knew her best, and from those who want to protect her memory and want to remind people of the person that she was: The warmth, the humor, and what she was like as a mother, which probably hasn’t come across before in many other pieces from other people.”

Harry also revealed he has only cried tears of grief twice – at her graveside at Althorp on September 6, 1997, and since then “maybe, maybe once. ”

“So there’s, you know, there’s a lot of — there’s a lot of grief that still needs to be let out," he said.

Credit: Julian Parker/UK Press/Getty Images

Harry added, “There’s not a day that William and I don’t wish that she was still around, and we wonder what kind of a mother she would be now, and what kind of a public role she would have, and what a difference she would be making.”