The King's cancer treatment will continue into the New Year, Sky News understands.
Palace sources have said "his treatment has been moving in a positive direction and as a managed condition the treatment cycle will continue into next year".
The source added there is a sense of optimism, which can be seen in the King'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.
Very early on, the monarch personally took the decision to share his diagnosis, and his experience, in the hope it may help others.
But he has deliberately not confirmed the type of cancer he is being treated for so he doesn't detract from the significance of other forms of the illness.
It is also unclear what type of treatment he has specifically had, but he has regularly been in London for private appointments.
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."
Speaking more widely about the openness of both the King and the Princess of Wales, she added: "What we've heard from our centre visitors, it's been good that they haven't just shone a light on one specific cancer type, but they've shone a light on cancer as a whole, and that there's varying treatment and varying impacts and varying different ways of navigating the challenges that cancer bring.
"And I think that approach has been much more effective and positive for the cancer community. I know firsthand that everyone is so grateful to them for doing that."
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Later, the King and Queen will carry out their last big public engagement before they begin their Christmas break, meeting local community volunteers, young people, emergency services, and faith representatives in Waltham Forest.
For their final visit of the year they wanted to thank and celebrate communities who responded to the violent disorder that flared up in the summer following the Southport stabbings.
The royal couple will talk to some of the Waltham Forest residents who attended a peaceful anti-racism protest in early August, demonstrating the true community spirit of the borough.
Waltham Forest has been officially recognised as a Borough of Sanctuary, meaning it values and celebrates the migrants, refugees, and people seeking sanctuary who have settled there.
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Their visit comes as palace sources told us "the intention is for the monarch to return to a full programme of public duties next year", with planning for the first half of the year involving "an exciting mix of national and international events".
At the end of their tour of Australia and Samoa, a senior palace official said the trip had lifted the King's spirits, his mood, and his recovery, and that they were "working on a pretty normal-looking full overseas tour programme for next year".
The source added a fuller schedule "is a high for us to end on, to know that we can be thinking in those terms, subject to sign-off by doctors".
We've also been told that despite everything that has happened this year, the King and Queen seem happier than they did at the end of last year, partly perhaps because they are more settled in their new roles, but also because of the outpouring of kindness they have received from members of the public.
(c) Sky News 2024: King's cancer treatment will continue into next year, Sky News understands