The Monarch has filmed a first-hand account regarding his battle with cancer, set to air as part of this year's Stand Up To Cancer initiative, organised by medical research organisations and Channel 4.
Official sources confirmed the King would talk about his "recovery journey" as a cancer patient, in a televised statement on Friday evening at 8pm UK time.
The message, taped inside his London residence recently, will emphasise the critical nature of routine screenings to ensure more people detect the condition at an initial point.
This represents a uncommon insight on the wellbeing of the Monarch, who has been receiving ongoing care since his condition was announced in February 2024. However, it is believed unlikely the King will specify his specific form of cancer.
The awareness event each year generates donations for medical research and therapies and prompts people to get health assessments to improve the chances of an timely detection.
The King's candid approach about his illness, and managing the disease, has been aimed to increase understanding and to encourage more people to get tested - and this will be advanced with this unusual personal contribution.
So far the King's primary strategy to his cancer has been to maintain his duties, preserving a busy schedule despite his regular rounds of treatment, and he is understood not to have sought to be overshadowed by his diagnosis.
Recently has seen the King, 77, undertaking several overseas trips, including to Italy and Canada, and receiving the biggest number of inward state visits to the UK for almost 40 years, featuring the German president in recent days.
This Friday's charity broadcast on the network, featuring well-known figures like a team of famous hosts, will encourage people not to be frightened of getting health screenings.
Each presenter have been had experience with cancer - Davina McCall said in November she had undergone surgery for a tumour, while another presenter was overcame the illness more than 15 years ago. Host Hills has previously spoken about his father, who had one form of cancer and then later another illness.
The broadcast will reach out to the approximate nine million people in the UK who Cancer Research UK estimate are not up to date with public health checks, with an website to let people see if they are qualified for examinations for key health indicators.
In an attempt to demystify screenings and demonstrate the importance of prompt detection there will be a live broadcast from hospital departments at medical facilities in Cambridge.
"The goal is to take the fear from health checks and prove all people that they are not alone in this," said Davina McCall.
Right now in the UK, there are several key publicly available checks - for specific cancers - accessible for eligible individuals.
A new lung cancer screening programme is also being phased in for individuals at high risk of developing the condition, focusing on people aged 55-74 years old, who are smokers or used to.
Men may enquire about specific tests, but there is no national programme operational.
The charity project, which has generated £113m for many years, is funding dozens of research studies with 13,000 patients.
The Monarch, in a message for dignitaries at a event for support groups in April, had spoken of understanding the "overwhelming and at times frightening situation" for patients and their families.
But he noted his first-hand encounter of coping with cancer had demonstrated that "the darkest moments of illness can be alleviated by the greatest compassion," as he commended those who cared for those receiving treatment.
Royal representatives has not disclosed the nature of cancer the King has, or what treatment he has been given. The King's cancer was discovered following he had received a routine operation.
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