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(LONDON) -- King Charles III has made his first public appearance since Buckingham Palace announced he was diagnosed with cancer.

Charles, 75, and his wife, Queen Camilla, were seen attending church in Sandringham on Sunday.

On Monday, Charles began his cancer treatment and the palace announced his diagnosis.

The palace has not specified the type of cancer, the stage of cancer or the type of treatment, but British Prime Minister Rishi Sunak told the BBC that the king's cancer was "caught early."

"I would like to express my most heartfelt thanks for the many messages of support and good wishes I have received in recent days," the king said in a statement Saturday. "As all those who have been affected by cancer will know, such kind thoughts are the greatest comfort and encouragement. It is equally heartening to hear how sharing my own diagnosis has helped promote public understanding and shine a light on the work of all those organisations which support cancer patients and their families across the U.K. and wider world. My lifelong admiration for their tireless care and dedication is all the greater as a result of my own personal experience."

Charles was advised to postpone all his public-facing duties but will continue his state business and official paperwork, according to the palace.

Prince Harry, who lives in California, traveled to London this week to see his father, staying in the United Kingdom for about 24 hours before heading back to the U.S.

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