Dame Sue Bruce said he had asked after her seriously ill husband last week, shortly before the Queen’s death.
Dame Sue is chairwoman of the board of trustees at the Prince’s Foundation, an educational charity which promotes sustainable practices.
She spoke to reporters at Dumfries House in East Ayrshire, the charity’s headquarters.
The 18th century building and its 2,000-acre estate were purchased by a consortium in 2007, with a new walled garden and educational farm being added later.
Dame Sue said that while he was Prince of Wales the King had played a key role in preserving the estate for the nation, and it is now frequently used by the local community near Cumnock.
She said: “Under his convenership, a great deal of people came together and worked with the prince to conserve this place.
“Stories I’ve heard from people locally is that people were able to look through the gate but were never able to come in.
“Under the prince’s vision and inspiration, it’s been developed – with various schools, activities and so on.”
The King enjoyed his visits to Dumfries House, she said, adding: “The King has a great affinity with Scotland.
“He loves it here at Dumfries House, he loves it in Deeside.
“But of course he’s also a man of the country and the countryside.”
She said Charles would often stop to chat to people while walking around the estate.
Dame Sue said: “The prince is very personable, he’s easy with people, he’s a kind and caring individual and he will be concerned as much for how others feel at the loss of her late Majesty the Queen as much as people are concerned about his loss.”
She expects the King will remain interested in the work of the foundation, which will continue to provide him with updates.
Asked what kind of leader she thinks he will be, Dame Sue said: “I think he will be a very good monarch.
“He’s clear in his ideas, he’s a really caring person, and those of us who are fortunate to have worked with him in first-hand have seen that.
“He’s got an enormous appetite for work.
“He likes things to be done. If you say you’ll do things, he expects them to be done.”
Charles was at Dumfries House last week for the Global Allergy Symposium.
Those who know him personally find him to be “incredibly considerate”, Dame Sue said.
She continued: “A personal story from me, my husband has been quite seriously ill. I’ve had several inquiries from the King about how he’s doing.
“In fact, when I met him last week the first thing he said was ‘how is your husband?’
“Thankfully I was able to tell him he’d made good progress.
“He’s a warm individual, a caring individual, and I’m quite sure that will come through in his reign as monarch.”