King Charles' health is said to be heading in a "very positive" direction

A source told the Daily Mail Charles has also coped with the past year - which has also seen his daughter-in-law Catherine, Princess of Wales, 42, have preventative cancer treatment - with a "determination to be as public as he was able" about his fight to reassure the nation about his capabilities as king.

The insider added: "Health has to remain the number one priority, albeit heading in a very positive trajectory."

Charles and Camilla, 77, are set to go on a tour of Australia and Samoa in the autumn.

It will mark their first major overseas trip since news of Charles' cancer was broken.

Camilla has been undertaking public royal visits in the last year and has repeatedly told royal fans during the trips Charles is strong and fighting back.

She gave her latest insight into Charles' treatment this week when she opened a cancer centre in Bath - saying he is doing "very well".

The source said about how Camilla's support was helping Charles: "Her natural warmth, resilience and sense of humour, as I'm sure any patient will tell you, is a wonderful thing to have.

"Of course, it's been a stressful year for Her Majesty, too, but there was never a sense of despondency, only a determination that they would get through this, as with so many other challenging issues in the past."

Charles stayed away from public duties for around three months after he was diagnosed with cancer in January.

He returned to work in April with a visit to a cancer centre in London where he met with fellow patients, and insiders say "down time" is set to be incorporated into his and Camilla's visit to Australia and Samoa.