Actor Damian Lewis gave the Prince of Wales a history lesson on the monarchy as the pair discussed his role as Henry VIII at a charity dinner.
Charles was greeting guests at his annual Invest in Futures Gala dinner to raise cash for the Prince's Trust when Lewis made the quip.
As they talked about his role as Henry VIII in the TV adaptation of Hilary Mantel's Wolf Hall, the actor said: "You know he invented 'Your Majesty'? No monarch before Henry VIII was 'Your Majesty', because monarch wasn't enough."
Charles laughed as Lewis doffed an imaginary cap to him, joking: "They teach us to read and everything, Sir!"
His wife, actress Helen McCrory, added after the exchange: "Only my husband could give the future King of England history lessons on the monarchy."
The star-studded evening at Old Billingsgate, central London, was also attended by James Bond actress Naomie Harris, boxing champion David Haye and newly-engaged supermodel Jerry Hall, while Kylie Minogue performed.
Charles told guests: "I met Kylie a long time ago - her voice and movements get better and better each year."
Thanking them for coming to the event, he joked: "It isn't easy to get here, even with the odd motorbike. I have a feeling you all had to set off around lunchtime."
Haye, who was attending his first event as an ambassador for the trust, said he discussed his recent victory in the ring with Charles, who seemed up to speed on the sport.
He told the Press Association: "I met the big man, he knows his boxing. He didn't see my last fight but he will be watching the next one.
"I told him he should come down and I will get him a couple of ringside seats. That would be quite some support.
"I told him I'm going to be world champion again and he's backing me all the way."
Haye added: "I'm looking forward to hearing about how the Prince's Trust has helped people turn their lives around.
"Sometimes it takes someone who has had success at a high level to give you that push.
"I remember meeting Frank Bruno when I was 10 years old and him telling me, 'You could do this, you could be a world champion' – that made a big impression."
Many other famous faces were there to show their support for the trust, including offering their skills or items for the secret auction.
Former Spice Girl Geri Horner was on the bidding lot for her cake baking skills - with her cooking abilities fetching hundreds of pounds in bids.
She said: "I think it is amazing how many years the trust has been going - I think it is incredible.
"I love that it is empowering people, I think it is fantastic that the Prince of Wales has continued and put that effort into it."
She also said it was too early to say anything about the Spice Girls reunion, but that Victoria Beckham would not be taking part, and she definitely would not be pinching the Prince's bottom again.
The trust, which celebrates 40 years this year, helps disadvantaged youngsters turn their lives around - offering support and advice to those in need.
Lewis said: "For some young people it's a close run thing between success being made possible by the Prince's Trust or going to jail. It's vital."
McCrory added: "They embrace people with mental health issues. When you've tripped and fallen and there is no one else to turn to, the Prince's Trust has never shied away from that. Everyone is given a chance."
The gala event, which is now in its 11th year, has so far raised more than £17.5 million for the charity.
The evening was hosted by Hugh Dennis and Joanna Lumley, who told the Press Association: "I have seen the massive difference the trust makes. I've talked to the young people and the confidence it gives them.
"It is not just a one off, the trust is there to mentor them, advise them and support them - always to be there if something goes wrong or if they slip off the rails.
"And their despair is turned into hope. Prince Charles, the highest in the land has said, we are here, we can help."
The trust has over the years supported famous faces such as actor Idris Elba and magician, Dynamo.
Hall, who recently became engaged to media magnate Rupert Murdoch, has been an ambassador for 30 years, said: "I love Prince Charles – preserving the environment, protecting historic buildings and helping young people – he's wonderful."