“The Queen put an invisibility shield around the royals – no one wanted to disrespect her or question her dedication to duty.”

Endgame was released last month and makes a series of sensational claims about the royals, and saw the Princess of Wales’s workload criticised, however, no member of the Royal Family has responded to the attacks.

Kate is dubbed “Katie keen” and is also described to be “cold and vacant” who had ignored Meghan Markle’s “cry for help”.

The PR expert went on to say Kate kept strong, in the aftermath of the book, following the late monarch’s key rule of “never complain, never explain”.

She said: “The Queen was a strong, powerful woman who was respected globally. And we now see Kate emerging as this Queen in waiting, who is just as strong and powerful.

“Her dedication to duty and work with charities has not only made her hugely popular with the public, but respected too. And I think it’s this level of respect and class – similar to what the Queen had – that is getting the royal family through [these claims].”

“Kate is following the Queen’s key rule of ‘never complain, never explain’ and is carrying on with her daily duties. We have seen her out and about, at important engagements, smiling, and showing the world she is strong – and that’s the shield. It’s a shield of strength and stoicism really.”