Charles's pre-recorded message, which will stress the importance of the cancer screening program to help early diagnosis, will be broadcast on Saturday AEDT as part of a campaign by Cancer Research UK and Channel 4.
There has not been an official update about the King's state of health for some time but in May, during a discussion with a well-wisher about his wellbeing, the UK monarch said: "I'd like to think I'm on the better side (of my cancer journey)."
The King's message will broadcast at 6am AEDT and was recorded in late November.
Charles' cancer diagnosis was announced on February 6, 2024 and he postponed all public-facing engagements for a period.
The previous month, Charles spent three nights in hospital for a procedure on an enlarged prostate, during which time his cancer - not prostate cancer - was discovered. The exact disease has not been disclosed.
Charles marked his return to in-public royal events in April last year by visiting University College Hospital Macmillan Cancer Centre in central London and spoke of his "shock" at being diagnosed when he chatted to a fellow cancer patient.
The King has been receiving his cancer treatment as an outpatient since early February 2024, believed to be weekly sessions at the London Clinic.
Charles stepped up his workload at the start of this year following positive progress with his cancer care and that has continued, despite what a source described at the time as a "minor bump" of spending a short stay in hospital after experiencing temporary cancer treatment side effects in March.
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