Harry recalls her sense of mischief, and says: "Her motto to me was: you can be as naughty as you want, just don't get caught".
The princes, who were 15 and 12 respectively when their mother died in a Paris vehicle crash on August 31, 1997, told filmmakers they only had a brief phone call with the holidaying princess because they wanted to return to playing with their cousins. "If I'd known now, obviously, what was going to happen I wouldn't have been so blasé about it and everything else", William said in the documentary while he and Harry were looking through a photo album.
On Monday, HBO will release a new documentary marking the 20th anniversary of Princess Diana's death, offering personal insights into the lives of Prince Willam and Prince Harry and the pain they experienced after learning they'd never speak to their mother again.
"And then funnily enough, we got to the age when William would turn round and go, 'Oh, this is ridiculous, you know, I'm the older brother, why do I have to be dressed the same as him?' And I'm sort of sitting there going hang on a second, if you're going to dress differently I'm not going to be the only person dressed like this - this is just ridiculous", he said.
He said the Princes bare all. "That phone call sticks in my mind quite heavily".
'I haven't experienced many people in my life who have that ability.
Prince William was just 15 and his brother Harry 12 when their mother and her boyfriend Dodi Al-Fayed were killed in August 1997 after the auto they were in crashed in a tunnel in central Paris as it was being pursued at high speed by press photographers.
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Senators Susan Collins of Maine, Lisa Murkowski of Alaska and Shelley Moore Capito of West Virginia are opposed to repeal. However, it looks likely to fail after the defections on Tuesday of at least three of the party's senators.
"Our mother was a total kid through and through".
"So I like to think that she had great fun in dressing us up", Harry said.
Diana, Our Mother: Her Life and Legacy will air Monday at 10 p.m. on HBO in the USA and 9 p.m.in the United Kingdom on ITV.
With Prince William and Prince Harry seen as a modernising force at the palace, it seems the effect is still being felt.
Prince William also shared a story about when Diana surprised him with a meeting with his favorite supermodels.
"I was probably a 12 or 13-year-old boy who had posters of them on his wall". "She'd love the children to bits, but she'd be an absolute nightmare". Rather, they wanted to cover new ground and make a different type of film. "And sort of fumbled and I think pretty much fell down the stairs on the way up".
The program is one of a series of tributes to Diana expected as the 20th anniversary of her death approaches.