The King was described as being in “good spirits“ by double world heptathlon champion Katarina Johnson-Thompson as he presented her with an MBE.
Charles returned to official public duties after cancelling a string of engagements at the end of last week, when he experienced temporary side effects from cancer treatment on Thursday.
The athlete was recognised for an outstanding track and field career during the Windsor Castle ceremony hosted by Charles.
Gardener and broadcaster Alan Titchmarsh also praised the King for his “boundless energy” despite his cancer diagnosis, as he was made a CBE.
The King welcomed dozens of recipients to Windsor Castle after spending a restful weekend and working on state business on Monday.
Johnson-Thompson said after the ceremony: “He seemed in good spirits. You know it’s long, all day, because so many people are getting honoured today.
“So he seems in really good spirits and I’m happy to see that he’s fit and well.”
Johnson-Thompson is the reigning world heptathlon champion winning gold in 2023, four years after she first won the title.
She came back from a serious Achilles injury in 2020, which left her fearing for her career, to win silver at the Paris Olympics last year.
Asked about her conversation with the King, the Liverpool athlete said: “We were just chatting about… the toll that athletics puts on, or sports puts on the human body, and just how long I’ve been doing it.
“He also mentioned that you need a good physiotherapist”.
Titchmarsh has been a mainstay on British television for decades appearing in programmes like Gardeners' World and Ground Force, and also presenting documentaries alongside a flourishing writing career which includes a number of novels.
He said after the ceremony: "It's 61 years now that I've been gardening for a living, but just trying to enthuse people, share a passion and to explain how gardening is the sharp end of conservation and caring for the landscape.
"It also offers wonderful solace and peace of mind to all of us in really challenging times."
The gardener said about the King: "Anybody who knows him at all, who's worked with him, is just in awe of his boundless energy - that's without the issue that he's had.
"He is so energetic, he's not just a talker, he's a doer."
Describing the King as "tremendously loyal", Titchmarsh said they had been friends for 40 years and that he does not offer gardening advice to Charles, but they just chat as friends about their shared passion.
He said about his brief conversation with Charles during the ceremony: "He very kindly said I'm climbing up the ladder, which was nice of him - from MB
