Speaking about Kate’s parents, Jennie said: “They are quite obviously an integral part of the family and have undoubtedly been a source of enormous strength for Catherine through these past difficult months.”

She added: “I always feel for Carole and Mike in all this, because this is their little girl who is facing a shocking and life-changing illness. While Catherine has been worrying about her own children, the Middletons have, I’m sure, been worrying about their darling daughter – as well as their grandchildren.”

The former royal correspondent also described the relationship Prince William has with Kate’s side of the family, explaining he can “relax” and “be himself” in their company.

Although Kate’s bother James and sister Pippa did not make an appearance in the footage, the royal expert stressed they were all a “tight family unit”.

Pippa Middleton was also spotted alongside Kate and her daughter, Princess Charlotte, during the Wimbledon Men’s Final this summer – Kate’s second official public appearance of the year.

In the video, which showed snippets of the family’s summer holiday, The Princess of Wales gave fans a behind-the-scenes look at family life with Prince William and their three children Prince George, Princess Charlotte and Prince Louis.

The video comes just six months after Kate released a video from Windsor Castle where the princess announced she had been diagnosed with cancer and was undergoing treatment.