The King waved to onlookers as he walked to St Mary Magdalene’s church on the monarch’s Sandringham estate in eastern England on Sunday morning.
Earlier this week he was photographed in the back of a car on his Sandringham Estate.
On Monday, Buckingham Palace announced Charles, 75, had been diagnosed with an undisclosed form of cancer and will step back from public-facing duties while he undergoes treatment.
It was identified after he was admitted to a London hospital for a corrective procedure for an enlarged prostate last month, said the palace. Prostate cancer has been ruled out to CNN by a royal source, who did not provide any further detail.
He was advised by doctors to step away from public-facing duties, but the palace stressed he would continue state duties and paperwork.
Charles is expected to carry on getting his daily red boxes with government papers so he can continue working through state documents at home. CNN understands it is anticipated the King will continue his weekly audience with the prime minister and alternative arrangements will be made if his doctors advise him to minimize in-person contact.
Prince William, Charles’ son and the heir to the throne, and Queen Camilla are expected to take on more public engagements to account for Charles’ absence.
Meanwhile, his son Prince Harry made a brief visit to the UK earlier this week after Charles’ diagnosis.
Harry then appeared at the NFL Honors award ceremony in Las Vegas on Thursday, presenting the Man of the Year award.
In his first public comments since his diagnosis, Charles expressed gratitude to the public for their support, saying it brought him “the greatest comfort and encouragement,” according to a statement on Saturday.
Mitchell McCluskey and Tara John contributed reporting.
