“When you think of the personal revelations, and I think you can call them snide remarks made about Kate in Spare, Harry broke the one rule and that is staying silent on family matters.”

In his tell-all memoir, which was released back in January, Prince Harry discussed the royal feud calling her the “sister I’ve never had and always wanted”.

Katie Nicholl said, “While Kate and Harry used to be very, very close, there’s been a complete breakdown of that relationship. I don’t think Kate does angry. I think it is more a case of feeling very disappointed, very let down and feeling hurt knowing that she had no right of reply – and Harry knew full well she had no right of reply.”

Unlike his wife, the royal expert explained that Prince William was “very angry” at his brother for dragging Kate Middleton into it, feeling that she was “blameless throughout”.

“[Kate] acted very much as the peacekeeper, she tried to get the brothers back on an even keel and for Kate to be dragged into this mucky saga was upsetting for her and certainly did infuriate William,” she said.

Talking of Meghan Markle, the royal expert said, “I think it’s too far down the line for Kate and Meghan. There were some deeply personal revelations about Kate in the book.”

“Meghan clearly didn’t enjoy her time here [in the UK] and she’s obviously leading a much happier life in California. She is certainly in no hurry to come back to Britain [to reconcile], though she was certainly in a hurry to leave!”