He told PEOPLE: “[King Charles] is a father who loves his son and a doting grandfather.

“One thing we don’t see, and people weren’t expecting, the King is spending a lot more time at Windsor than anyone expected.”

“He’s often there on Thursdays and Fridays. Obviously, the Waleses are within walking distance of the castle.

“He’s never really had that sort of proximity to the younger family. Now, there’s more overlap.”

The author also commented on the closeness of the family, stating: “Like all families, they’ll have their moments, but there is clearly a sense of common purpose. They all realise this is a team effort.”

He added: “I think very much it’s parents first. If he was asked to, I mean, he’d be delighted, but I think it’s very much parent-driven. We haven’t got to that.

“I suspect the time will come rather like that sweet rapport between the late Queen and Prince William, but I suspect not yet.”

The short distance between Adelaine Cottage and Windsor Castle will be a welcome addition when Princess Kate is back from the hospital, after being admitted for a successful abdominal surgery earlier this week.

Kate is said to continue her recovery until Easter at home.

Meanwhile, the King is due for an enlarged prostate operation next week but Queen Camilla said on Thursday that Charles is “looking forward to getting back to work.”