The Monarch has filmed a intimate address concerning his battle with cancer, set to air as part of this year's Stand Up To Cancer drive, organised by medical research organisations and a major network.
Buckingham Palace said the King would talk about his "healing process" as a person living with the disease, in a recorded address on Friday at 20:00 GMT.
The address, recorded at his London residence a fortnight ago, will highlight the importance of routine screenings to help guarantee more people diagnose the condition at an treatable phase.
This will be a rare update on the medical condition of the King, who has been receiving ongoing care since revealing his diagnosis in February 2024. But it is thought improbable the King will specify his particular diagnosis.
The annual charity initiative each year generates donations for clinical trials and treatment and urges people to get check-ups to boost the chances of an early diagnosis.
The King's public discussion about his health challenge, and living with cancer, has been intended to promote education and to persuade more people to get tested - and this will be escalated with this exceptional royal involvement.
To date the King's key philosophy to his cancer has been to keep working, maintaining a hectic timetable alongside his frequent sessions of therapy, and he is understood not to have desired to be characterised by his illness.
This year has seen the Sovereign, undertaking several foreign visits, such as visits to Italy and Canada, and welcoming the biggest number of foreign dignitaries to the UK for a generation, featuring the German president last week.
This Friday's Stand Up to Cancer programme on the network, presented by presenters including a team of famous hosts, will urge people not to be scared of getting cancer checks.
All three have been had experience with cancer - Davina McCall disclosed in November she had undergone surgery for breast cancer, while Clare Balding was diagnosed with thyroid cancer over a decade ago. Comedian Adam Hills has previously discussed his father, who had one form of cancer and then later blood cancer.
The programme will target the estimated 9m people in the UK who charities says are not compliant with national health programmes, with an website to let people check if they are qualified for screenings for breast, bowel and cervical cancer.
In an attempt to clarify screenings and show the benefit of prompt detection there will be a direct feed from cancer clinics at two Cambridge hospitals in Cambridge.
"The goal is to remove the anxiety out of preventative tests and prove the public that they are not isolated in this," stated Davina McCall.
Currently in the UK, there are three publicly available checks - for specific cancers - accessible for certain age groups.
A new preventative initiative is also being phased in for anyone at potential risk of being diagnosed with the disease, focusing on people in a specific age bracket, who currently smoke or used to.
Individuals may enquire about specific tests, but there is no national programme in place.
The Stand Up to Cancer initiative, which has generated £113m since 2012, is supporting 73 medical projects involving thousands of patients.
His Majesty, in a address for attendees at a event for support groups in earlier this year, had spoken of acknowledging the "daunting and at times alarming experience" for patients and their families.
But he said his first-hand encounter of managing cancer had revealed that "periods of great challenge of illness can be illuminated by the support of carers," as he commended those who supported individuals with the illness.
Royal representatives has not revealed the specific type of cancer the King has, or the medical care he has undergone. The King's cancer was identified subsequent to he had had a medical treatment.
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