The Monarch has recorded a intimate address concerning his journey with cancer, which will be broadcast as part of this year's annual cancer awareness initiative, run by a leading cancer charity and Channel 4.
Official sources said the King would talk about his "path to recovery" as a individual battling cancer, in a recorded address on Friday at 20:00 GMT.
The message, taped inside his London residence two weeks ago, will highlight the vital significance of cancer screening checks to ensure more people catch the illness at an early stage.
This will be a rare update on the wellbeing of the Sovereign, who has been receiving ongoing care since revealing his diagnosis in February 2024. However, it is believed unlikely the King will disclose his type of cancer.
The awareness campaign each year collects money for scientific studies and therapies and encourages people to get health assessments to improve the probability of an prompt identification.
The King's public discussion about his illness, and managing the disease, has been intended to increase understanding and to get more people to get tested - and this will be taken a step further with this unique personal contribution.
So far the King's primary strategy to his cancer has been to continue his schedule, maintaining a full diary despite his regular rounds of treatment, and he seems not to have wanted to be characterised by his condition.
Recently has seen the Sovereign, taking several overseas trips, including to Italy and Canada, and welcoming the largest volume of official guests to the UK for decades, including the German president in recent days.
Friday evening's charity show on Channel 4, hosted by presenters like a team of famous hosts, will appeal to people not to be scared of getting preventative tests.
Each presenter have been had experience with cancer - one host revealed in November she had received treatment for a tumour, while another presenter was overcame the illness over a decade ago. Presenter Adam Hills has previously mentioned his parent, who had a diagnosis and then later blood cancer.
The broadcast will appeal to the roughly 9m people in the UK who Cancer Research UK says are not up to date with public health checks, with an online checker to let people determine if they are qualified for screenings for key health indicators.
In an effort to explain health tests and illustrate the benefit of timely identification there will be a real-time transmission from hospital departments at Addenbrooke's and Royal Papworth hospitals in Cambridge.
"I want to reduce the stigma surrounding health checks and demonstrate everyone that they are not isolated in this," stated one of the hosts.
At present in the UK, there are three national health screening services - for bowel, breast and cervical cancer - accessible for certain age groups.
A new scheme for lung health is also being phased in for people at potential risk of contracting the illness, specifically targeting people of a certain age, who are smokers or have smoked in the past.
Male patients may enquire about prostate screenings, but there is no national programme in place.
The Stand Up to Cancer campaign, which has raised a significant sum for many years, is funding 73 clinical trials with many patients.
King Charles, in a message for attendees at a event for cancer charities in April, had referred to acknowledging the "intimidating and at times frightening situation" for those diagnosed and their support networks.
But he said his personal journey of coping with cancer had demonstrated that "the darkest moments of sickness can be alleviated by the greatest compassion," as he thanked those who cared for individuals with the illness.
Official sources has not revealed the nature of cancer the King has, or the therapies he has been given. The King's cancer was identified subsequent to he had had a medical treatment.
Elara Vance is a tech journalist with over a decade of experience covering emerging technologies and consumer electronics.