"The first time I met her I was with my mum at a club. I actually said to her, 'I'm here with my mum and my mum loves you. She would love to meet you.' And she was like, 'Oh, OK.' My mum spent about 20 minutes with her chatting and I suppose the rule is if someone's nice to your mum they really go up in your estimation."
The Karma Chameleon singer described Diana as "sweet" and "gracious", but above all, he said she was just "good fun".
"I was at a charity lunch with her and Wayne Sleep [a British ballet dancer]. He was quite drunk and he was falling on her and I thought, 'Oh my god, they're going to chop his head off in a minute!'"
But Diana was unfazed by the inappropriate behaviour and laughed it off.
"At one point she just looked at me and rolled her eyes and started laughing," Boy George said.
"It was so sweet and she was just a lovely woman."
PRINCE
Moving on from actual royalty to music royalty, Boy George also told us about his "really strange" encounter with Prince.
"When you meet someone like Prince, you don't want them to be like everyone else. He was really odd and I quite liked that.
"It was in Italy and I was doing a job for the Versace's and I was sitting at a table with him and all these people that didn't speak English, so you can imagine how awkward it was. I remember walking away thinking, 'Oh my god, that was really strange'."
But no matter how "awkward" the interaction was, Boy George said it didn't tarnish his opinion of Prince, whom he described as "a genius".
"I always say to people that there are certain artists that get a free pass, that I think, 'I love you so much that even if you're the weirdest person I've ever met it doesn't change anything for me.' And definitely Prince would be in that category."
ELTON JOHN
"I have been to Elton's house many, many times," Boy George said.
"Elton is hilarious and foul-mouthed. He doesn't hold back, he definitely says what he thinks."
The last time Boy George caught up with Elton was at the music superstar's house for his birthday party last year.
"I was sitting with Elton on one side and Kate Bush in front of me," he said, "That was pretty amazing".
So what's a party at Elton's like?
"It's a lot of fine dining and luxury, he's got a beautiful home," Boy George said.
"He's got this amazing art gallery in his garden and it's only about five per cent of the art that he's got."
Boy George is currently in Australia for his role as a coach on Channel Nine's The Voice.
The British singer has proved to be a hit with viewers and has won a whole new generation of fans, especially young ones.
And he's just teamed up with the YMCA Australia to record a new version of the famous song of the same name which he hopes will help give those young Aussie fans more of a say about some of the most divisive issues in our country right now.
"There actually is an incredible depth to young people when you start communicating with them and I've been really inspired by that," he said.
"One of the things I've learned since working on this project, I've been chatting to lots of young people from the YMCA, and what I like about young people is that on important issues they don't have the same filter as older people. For things like marriage equality, to them it's just really black and white, they don't have an issue with it.
"Young people are the future so we need to give them a voice regarding things like marriage equality, mental health, unemployment, all of those things."
