This file photo shows Kate, Britain's Princess of Wales, in a coach following the coronation ceremony of Britain's King Charles III in London, Britain, on May 6, 2023. Kate said on Friday that she has been diagnosed with cancer and is undergoing chemotherapy. [Photo/Xinhua]

The United Kingdom's (UK) Princess of Wales said on Friday that she has been diagnosed with cancer and is undergoing chemotherapy.

In a personal video message posted on X (formerly Twitter), 42-year-old Princess Kate said that tests after her planned abdominal surgery in January had found cancer.

"This of course came as a huge shock, and William and I have been doing everything we can to process and manage this privately for the sake of our young family, " she said.

"It has taken me time to recover from major surgery in order to start my treatment," she said.

The princess described having her husband Prince William by her side as a "great source of comfort and reassurance."

Kensington Palace said it would not be sharing the type of cancer, adding: "The princess has a right to medical privacy, as we all do."

According to the palace, the princess's chemotherapy began in late February, although it is unclear when it will end, and therefore when the princess will return to official duties.

The princess has not been seen on official engagements since late December, when she was pictured on a Christmas Day walk with other members of the Royal Family in Sandringham, Norfolk.

The announcement of Kate's illness comes less than two months after King Charles III, 75, also announced he had been diagnosed with cancer.

Following Kate's statement, Buckingham Palace said the King is "so proud" of the princess for her courage in speaking out as she did, and remains in the "closest contact with his beloved daughter-in-law."

Buckingham Palace said King Charles and Queen Camilla "will continue to offer their love and support to the whole family through this difficult time."

Prime Minister Rishi Sunak said Kate has shown "tremendous bravery", and has the "love and support of the whole country as she continues her recovery."

"I know I speak for the whole country in wishing her a full and speedy recovery and look forward to seeing her back in action when she's ready," Sunak said in a statement shared on X.