Britain’s King Charles III on Saturday expressed gratitude to well-wishers following his cancer diagnosis, his first public comment since Buckingham Palace announced he would postpone some engagements to undergo treatment.

“I would like to express my most heartfelt thanks for the many messages of support and good wishes I have received in recent days,” Charles said in a statement.

The palace announced on Monday that Charles, 75, had been diagnosed with a form of cancer, less than 18 months into his reign.

“As all those who have been affected by cancer will know, such kind thoughts are the greatest comfort and encouragement,” Charles said.

The king said it was heartening to hear how his diagnosis had helped to shine a light on the organizations that support cancer patients in Britain and elsewhere.

Charles attended church on Sunday in his first public outing since the diagnosis. Wearing a brown overcoat and carrying an umbrella, the king waved as he arrived with his wife, Camilla, at St Mary Magdalene church in Sandringham in eastern England.