The king, wearing a brown overcoat and carrying an umbrella, waved as he arrived with his wife, Camilla, at St Mary Magdalene church in Sandringham in eastern England.
Buckingham Palace announced on Monday that Charles, 75, had been diagnosed with an unspecified form of cancer. The king has been on the throne for less than 18 months following the death of his mother Queen Elizabeth.
Charles, who is spending time at his rural Sandringham estate, issued a message on Saturday expressing gratitude to well-wishers following his diagnosis.
“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 message stated.
“As all those who have been affected by cancer will know, such kind thoughts are the greatest comfort and encouragement,” he wrote.
“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 UK and wider world. My lifelong admiration for their tireless care and dedication is all the greater as a result of my own personal experience.”
While undergoing treatment, Charles has postponed public engagements but is planning to continue with much of his private work as monarch including having his weekly audience with the prime minister and dealing with state papers.
The cancer was discovered when Charles stayed three nights in hospital last month, undergoing a corrective procedure for a benign enlarged prostate. Beyond confirming it was not prostate cancer, the palace has not given any further details.
