When it comes to royal family nicknames, the Windsors are a creative bunch, but the Queen's son, Tom Parker Bowles, has chosen a more traditional moniker for his stepfather, the King.
Food critic and writer Tom, 49, is Camilla's son from her first marriage to Andrew Parker Bowles.
Camilla, who has known Charles since their younger years, married the then Prince in 2005.
In an interview with The Telegraph in 2012, Tom spoke about his relationship with his stepfather, confirming that he calls Charles "Sir".
"But it's not any sort of obligation, it's just a nickname really, like Bob or Jim," he told the newspaper at the time. "When we were little, my mother would tell my sister and I that Sir was coming to visit, so the name stuck and to call him anything else would be very odd and unnatural."
Tom and his sister, Laura Lopes, were among the guests at Charles and Camilla's wedding and blessing in Windsor, along with their stepbrothers, Prince William and Prince Harry.
© GettyLaura shares daughter Eliza and twin sons, Gus and Louis, with her husband, Harry, while Tom has daughter Lola and son Freddy with his ex-wife, Sara Buys.
Gus, Louis and Freddy all acted as pages of honour at the King's coronation in May 2023.
Ahead of the coronation, Tom hit back at claims that his mother played an "end game" to become Queen – saying she "just married the person she loved".
© James Veysey/ShutterstockSpeaking on The News Agents podcast in April 2023, he said: "I think change happens but I don't care what anyone says – this wasn't any sort of end game. She married the person she loved and this is what happened."
And paying tribute to his stepfather Charles, he added: "I think they're doing amazingly. I think King Charles is a good, kind, intelligent man who cares deeply about his roles wherever they may be, Prince of Wales, the King."
© GettyTom and Laura have not been given any titles since their mother became Queen.
The siblings have appeared at a number of high-profile events with the royals over the years, including Royal Ascot, royal weddings and Trooping the Colour.
© GettyAuthor Tom was seen sharing a warm embrace with the King at Royal Ascot in June.
Born in London on 18 December 1974, Tom grew up in Wiltshire and was educated at Summer Fields School in Oxford and Heywood Preparatory School in Corsham. He later attended Eton College and Worcester College, Oxford.
