Diana, Princess of Wales with her baby sons, Prince William, Duke of Cambridge and Prince Harry of Wales. (Tim Graham/Getty Images/courtesy of HBO)

On Monday night, HBO offered a rare sight — an in-depth interview with Prince William, 35, and Prince Harry, 32, about their mother, Princess Diana. Almost exactly 20 years ago, Diana was killed in a car crash in Paris. There’s an upcoming wave of tribute specials marking the anniversary of her death, but HBO’s documentary “Diana, Our Mother: Her Life and Legacy” is the only one that features new interviews with her two sons.

Because it’s unusual to hear this much personal information from the two princes, who typically shun the press unless they’re promoting charities or on official palace business, here are some of their most illuminating quotes:

Harry: “I genuinely think she got satisfaction out of dressing myself and William up in the most bizarre outfits, normally matching. It was weird shorts and, like, shiny shoes with the old clip-ons. And looking back at the photos, it just makes me laugh. I just think, ‘How could you do that to us?!’ Funny enough, we got to the age when William would turn around and go, “This is ridiculous, 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.’”

The special was packed full of adorable family photos, and many featured William and Harry in matching clothes — incredibly cute and probably mortifying. It was the perfect way to illustrate that even though William and Harry are royalty, they were not immune to embarrassment from their parents.

Prince Harry of Wales, Prince William Duke of Cambridge, Diana Princess of Wales. (Jayne Fincher/Courtesy of HBO)

William: “There’s not many days that go by that I don’t think of her. Sometimes sad, sometimes very positively. I have a smile every now and again when someone says something and I think, ‘That’s exactly what she would have said,’ or, ‘She would have enjoyed that comment.’ They always live with you, people you lose. My mother lives with me every day.’”

Important note: You probably can’t make it through this documentary without crying.

Harry: “To myself and William, she was just the best mother ever. She would just engulf you and squeeze you as tight as possible – and being as short as I was then, there was no escape, you were there and you were there for as long as she wanted to hold you. Even talking about it now, I can feel the hugs she used to give us. I miss that. I miss that feeling, I miss that part of a family, I miss having that mother to be able to give you those hugs and give you that compassion that I think everybody needs.”

See? Impossible.

Diana with toddler Harry. (Tim Graham/Getty Images/Courtesy of HBO)

William: “She was very informal and really enjoyed the laughter and the fun, but she understood there was a real life outside palace walls and she wanted us to see it for a very young age.”

Diana brought her kids with her when she embarked on her charity work; for example, when she visited homeless shelters. To this day, William still goes back to visit residents.

Harry: “Our mother was a total kid, through and through. When everybody says to me, ‘So she was fun, give us an example,’ all I can hear is her laugh in my head. That sort of crazy laugh of where there was just pure happiness shown on her face. One of her mottos to me was ‘Be as naughty as you want, just don’t get caught.’”

She was determined for her sons to have as normal of a life as possible, despite growing up in the limelight at Kensington Palace — so she took them to eat burgers and sneaked them into movie theaters. She also had a “cheeky” sense of humor and pulled pranks, like when 13-year-old William came home from school and three famous supermodels (all of whom were on posters in his room) waited to greet him at the top of the stairs.

(Tim Graham/Getty Images/courtesy of HBO)

Harry, describing the final conversation he had with his mother: “I can’t really remember what I said. What I do remember is regretting for the rest of my life how short the phone call was. If I had known that was the last time I was going to speak to my mother, the things I would have said to her. Looking back on it now, it’s incredibly hard. I have to deal with that for the rest of my life, not knowing that was the last time I was going to speak to my mum, and how differently that conversation would have panned out if I had only the slightest inkling that her life was going to be taken that night.”

This revelation has received the most attention over the last few days. On the day Diana died, William (age 15) and Harry (age 12) were on holiday with their cousins and she called to check in from Paris. But like many boys their age, they were in a hurry to get off the phone. They still wrestle with the guilt of the abbreviated phone call.

Documentary producer: “How do you keep her memory alive for your children?”

William: “I think constantly talking about Granny Diana. [Laughs.] We’ve got more photos up around the house of her, and we talk about her a bit. It’s hard because obviously Catherine didn’t know her, so she cannot really provide that level of detail. So I do regularly, while putting George and Charlotte to bed, talk about her, and just try to remind them that there are two grandmothers – there were two grandmothers in their lives. And it’s important they know who she was and that she existed.”

Sorry, is it dusty in here? William also joked that Diana would have been a “nightmare” grandmother — the kind who loves her grandchildren so much that she would come over at night and disrupt their bathtime and make a mess because she just wanted to spend more time with them.

Harry, looking at an old photograph of him and William on the first day of school: “I was thinking, I’ve got my older brother at school, he’ll be looking look out for me — when in fact, you just ignored me.”

Ending on a lighter note — again, it proves royals are just like us.

Prince Harry of Wales, Prince William Duke of Cambridge. (Courtesy of HBO)