Grant Harrold, who worked as a butler for King Charles between 2004 and 2011, and also looked after the Prince and Princess of Wales when he was at Highgrove, has given fresh insight into what Catherine’s “secret power” is within the Firm. The former royal butler claimed that King Charles and Prince William are “really close” and, despite their different approach to some subjects, they “support each other”. He said that the King is “great at giving William advice and guidance,” and their heir has always been “very good at supporting his father”.

Mr Harrold said: “I think Princess [Catherine] is very good at grounding William, and she's very good at keeping him right and keeping him calm, which is what Queen Camilla's good at as well.

“I'd call her the power behind the throne, and what I mean by that is she's a very strong individual, but she's a real support.

“She's not a royal, but she's become a typical royal wife, which is what you want.”

It came as William and Catherine made a grand appearance at Royal Ascot this week, the first time the princess attended the annual racing event in two years.

Catherine last attended Royal Ascot in 2023.

The next year, she was diagnosed with a type of cancer and underwent treatment for it. She is now in remission.