“She did her bit, but it wasn’t enough to build a bridge between William and Charles on the one side and Harry on the other.”

Meanwhile, veteran royal commentator Richard Fitzwilliams agreed and told the outlet Kate is “totally at one” with her husband over his handling of the brotherly feud.

He said: “Harry portrayed her [Kate] as cold and unwelcoming to [his wife] Meghan Markle in Spare, when he painted an extremely damaging picture of the royal family.

“The memoir is soon to be released in paperback and his allegations will surface again, though fortunately, he will not be adding to the volume or promoting it. He knows perfectly well how damaging it has been.”

Spare is due to be released in paperback in the UK on October 24.

The expert added that the princess is now making a gradual return to royal duties as she now focuses on her health.

He said: “We have recently seen encouraging signs of Catherine’s recovery. Her focus, as she has said, is being ‘cancer-free’.”

The Princess of Wales announced the completion of her cancer treatment in an emotional video which was released last month.

Kate spoke about her cancer journey and said that she is now focusing on doing what she can to stay cancer-free, with a “renewed sense of hope and appreciation of life”.