In a new documentary marking the 20th death anniversary of Princess Diana which will be aired in the U.K. on Monday, Prince William and Prince Harry reveal some interesting details of their childhood years spent with their mother. Diana, who was a fun-loving mother, loved to surprise her children and the Duke of Cambridge speaks of one day when she surprised him by having three of the world’s top models waiting for him when he returned home from school, reports said.

William said in the documentary, the excerpts of which were released Sunday: "She organized when I came home from school to have Cindy Crawford, Christy Turlington and Naomi Campbell waiting at the top of the stairs. I was probably a 12- or 13-year-old boy who had posters of them on his wall." He added: "I went bright red and didn’t know quite what to say. And sort of fumbled and I think pretty much fell down the stairs on the way up," People reported.

He spoke of how the moment remained with him throughout his life and although it was embarrassing, it was a memorable, mischievous one with his mother. 

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The people's princess was just like a friend to her sons as she would tell her children "it’s ok to be naughty as long as you don’t get caught," Harry said. He also added one of the most vivid memories he has of Diana is the sound of her laughter.

The excerpts from the documentary also saw the younger son recalling how “naughty” his late mother could be when he was younger by sneaking him sweets at school. "She would come and watch us play football and smuggle sweets into our socks." At one point, Harry recalls "walking back from a football match and [hiding] five packets of Starburst... the whole shirt was just bulging with sweets."

Despite all the mischievousness, the late princess was a "very loving caring mother, and an incredibly funny person. A total kid, through and through," Harry added.

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However, the one memory which still haunts William and Harry is their last conversation with their mother, which was a very brief one. While Diana was in Paris, William was at Balmoral Castle in Scotland with his father, the Prince of Wales, along with other members of the royal family. William said: "At the time Harry and I were running around minding our own business, you know, playing with our cousins and having a very good time." He said that as a kid, he never enjoyed speaking to his parents on the phone.

“And we spent far too much time speaking on the phone rather than speaking to each other, because of just the way the situation [the divorce] was."

So, when the phone rang, William went to receive it. William added: “And I think Harry and I were just in a desperate rush to say goodbye, you know, see you later and we’re going to go off...If I’d known now obviously what was going to happen I wouldn’t have been so blasé about it and everything else. But that phone call sticks in my mind quite, quite heavily.”