The King has joked "I'm still alive" when asked how he was during an official royal engagement with the Queen.
It comes as palace sources told Sky News that his cancer treatment has been "moving in a positive direction... and will continue into next year".
The source added there is a sense of optimism, which can be seen in the monarch's desire to keep up a busy schedule of public engagements, including during the festive period.
Buckingham Palace announced in February that King Charles had been diagnosed with cancer and was beginning a course of treatment.
For their final visit of the year, the royal couple wanted to thank and celebrate communities who responded to the violent disorder that flared up in the summer following July's mass stabbing in Southport.
On Friday, the pair visited Walthamstow, in east London, after a peaceful anti-racist protest in the area in August.
The pair attended a reception in celebration of community cohesion at Waltham Forest Town Hall and greeted crowds who had gathered outside.
The King, 76, was asked "how are you?" by Sikh faith representative Harvinder Rattan. His Majesty smiled and replied: "I'm still alive."
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Dame Laura Lee, chief executive of the cancer support charity Maggie's - of which Queen Camilla is patron - said: "It's very common for treatment to be ongoing for very long periods of time, as is the treatment that the Princess of Wales went through, which is an intense period of treatment over a year, and then it comes to a point where it's on an end, and she's on that recovery from some of the impacts of her treatment.
"So we've got immunotherapy, chemotherapy, surgery, hormone therapy. There are all sorts of different treatment modalities. And so it's not surprising at all."
After disorder across some parts of the UK, thousands of people gathered in Walthamstow for a counter-demonstration on 7 August.
Among those greeting the royal couple in the town hall on Friday was Walthamstow MP Stella Creasy, who said the visit "means a lot".
During the visit, Camilla donated toys to Citizens UK, to be passed on to children living in asylum hotels, and a donation to a food bank was left on the King's behalf.
(c) Sky News 2024: King jokes 'I'm still alive' - as his cancer treatment to continue into next year