The King paid an unexpected visit to runners who were taking part in a local Sandringham parkrun for the second year in a row.
The parkrun, which was organised in partnership with the Move Against Cancer charity, saw runners shocked to see Charles watching from the sidelines on Saturday.
The jog was set up to support those living with and beyond cancer, as well as families, friends, and healthcare professionals.
His Majesty has been receiving cancer treatment as an outpatient since early February 2024.
King Charles surprised runners at parkrun event in Sandringham on Saturday
|PA
This is the second year in a row the monarch has surprised the Sandringham runners ahead of World Cancer Day on February 4.
In December last year, the head of state announced in a video message that his cancer treatment would be reduced, adding the “good news” was down to early diagnosis, successful care and following “doctors’ orders”.
The 5KYW run takes place on the last Saturday morning of every month and encourages anyone impacted by cancer to walk, jog, run, cheer or volunteer at more than 120 parkrun events across the UK and Ireland on the last Saturday of each month.
King Charles met runners with ambassador Sarah Byatt
|PA
Parkrun was founded in 2004 and, more than 20 years on, hundreds of thousands of people across 22 countries and five continents take part in free, weekly, timed five-kilometre running events each weekend in parks around the world.
The visit concludes a busy week for Charles, who premiered his new documentary Finding Harmony: A King's Vision in Windsor.
Kate Winslet, who narrates the documentary, posed for the camera, as did Beneditch Cumberbatch alongside his wife Sophie Hunter.
The visit is the second time the monarch has visited the parkrun, as he attended the event around the same time last year
|PA
Dame Judi Dench, Alan Titchmarsh and Sir Rod Stewart are also in attendance for the production's premiere.
Other celebrities who journeyed to Windsor include Formula One star Sebastian Vettel and actor Sir Kenneth Branagh.
The documentary, set to be released on Prime Video next month, focuses on the King's environmental campaign, despite years of fierce criticism.
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It looks back at the King's philosophy and lifelong commitment to green issues.
The 90-minute film shows His Majesty urging people to take a more serious approach to the climate, with mankind "actually destroying our means to survival".
He hopes there will be greater awareness of the issue, with a "need to bring things back together again".
The King and Queen attended His Majesty's documentary premiere this week
| PAThe King, in new footage, explained: "I just felt this was the approach that I was going to stick to. A course I set, and I wasn't going to be diverted from."
Charles previously warned that the approach to climate change is "rapidly going backwards," as the monarch shared his concerns.
He said: "People don't seem to understand it's not just climate that's the problem - it's also biodiversity loss, so we're actually destroying our means of survival, all the time."
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