King Charles is doing "extremely well", his wife Queen Camilla said on Thursday, in her first public engagement since the 75-year-old monarch was diagnosed with cancer.

Speaking to a well-wisher at a charity concert at Salisbury Cathedral, Camilla said Charles was touched by the messages of support from the public.

"He's doing extremely well under the circumstances," she said. "He's very touched by all of the letters and the messages the public have been sending from everywhere. That's very cheering."

On Wednesday, Prince Williamn thanked the public for their kind messages both about his father as well as his wife Kate following her recent surgery.

Kate, 42, underwent planned abdominal surgery on 16th January and then spent two weeks in hospital recovering.

Since then, Charles has undergone treatment for an enlarged prostate, before Buckingham Palace announced on Monday that subsequent tests on the monarch had revealed he had a form of cancer.

With the king postponing public duties to undergo outpatient treatment and Kate not expected to return to engagements until after Easter, the onus is on the remaining royals, especially William and Camilla, to provide the public face of the monarchy.