King Charles has been given an adorable nickname by Queen Camilla’s grandchildren.

While Prince George, 11, Princess Charlotte, nine, and six-year-old Prince Louis call the King “grandpa Wales”, Camilla’s grandchildren have a different name for the monarch. According to Tom Parker Bowles, he is known as “Uppa”.

Food critic Tom however says he sticks with a more formal approach when addressing his stepdad, instead opting to call him “Sir”. The Queen’s son, from her first marriage to former Army officer Andrew Parker Bowles, also revealed he still bows when meeting the King.

Speaking on the Times Royals podcast, Kate Mansey explained: “Tom Parker Bowles revealed he still calls Charles ‘sir’ and has done for years and is never going to change, calling his stepdad ‘sir’ but his children call him Uppa. It’s just a childhood, toddler-ish nickname they made up for him and it has sort of stuck. They just go ‘hi Uppa’ and he’s there sort of bowing.”

While the King is “Uppa”, Tom revealed children Lola, 16, and Freddy, 14, along with his sister Laura Lopes’ children, call the Queen “Gaga”. He revealed the King had been “wonderful” with the youngsters.

Speaking to People magazine, Tom said: “All of our children — my sister’s children too — have grown up with Gaga and Uppa. They've grown up from an early age knowing no different. [They know] Gaga as Gaga, and that she's a really great grandmother who occasionally spoils them in a good way.

“They adore the King because he is such a good, nice man. He has been a wonderful step-grandfather too; he has his own grandchildren, obviously. The children utterly adore him. From an early age, he’s read them stories, been there, and swung them around.”

Tom initially thought his children would have to bow when they met the King, with he and his sister both following the traditional royal protocol. However, the children soon adjusted to their famous step-grandfather, because Tom says he is “such a good man”.

He also revealed the children “didn’t know any difference” about the King’s royal heritage for the “the first 10, 12 years of their lives”. Instead he says they simply thought of Charles as “ the most kind, funny, sweet, step-grandfather”.

The King and Queen debuted their relationship together in 1999, with Camilla moving into Clarence House in 2003. They tied the knot in 2005.