The King is “so proud” of the Princess of Wales for her courage in speaking out about her cancer diagnosis and remains in the “closest contact with his beloved daughter-in-law”, Buckingham Palace has said.

Charles, who is also being treated for cancer, and the Queen have offered their love and support to Kate, the Prince of Wales, Prince George, Princess Charlotte and Prince Louis as the family try to come to terms with the news.

The monarch, 75, is extremely fond of the princess, who has been part of his eldest son the Prince of Wales’s life for more than 20 years.

Charles and Kate share a love of art, gardening and the outdoors – but now their bond sadly stretches to a shared cancer diagnosis and ongoing treatment.

The King and Queen were told the news about Kate’s health beforehand and were aware she was preparing to issue her video message.

Buckingham Palace said: “His Majesty is ‘so proud of Catherine for her courage in speaking as she did’.

“Following their time in hospital together, His Majesty has ‘remained in the closest contact with his beloved daughter-in-law throughout the past weeks’.

“Both Their Majesties ‘will continue to offer their love and support to the whole family through this difficult time’.”

The King, who acceded to the throne 18 months ago, is undergoing his own course of treatment for cancer, and Camilla said this week he was “doing very well”.

He is continuing his duties as head of state behind palace walls, conducting audiences and Privy Council meetings.

But he has postponed all public-facing engagements after beginning treatment for the undisclosed form of cancer in February.

He spent three nights in hospital for a procedure on an enlarged prostate, during which time his cancer – not prostate cancer – was discovered.