The King was left delighted as he spotted a "familiar face" in the crowds while meeting well-wishers during his arrival to Balmoral Castle on Tuesday.
In videos shared from the ceremony, Charles, 77, could be heard asking where everyone had travelled from. The visit was carried out just two days after the monarch was informed that his son Prince Harry and Meghan Markle would be returning to the UK with their family.
Some said they were from Cumbria, Glasgow and County Durham, while one person said they were from Aberdeen.
"Aberdeen, I don't believe it," the King exclaimed, delighted, before recognising the royal fan from previous visits.
© PA Images via Getty Images"Every Sunday, of course you do! It's so nice to see a familiar face. It's so courageous coming all that way."
The King appeared to be referring to his visits to Crathie Kirk for his regular Sunday church service near Balmoral.
King Charles, William and Kate arrive at Balmoral
The King was formally welcomed to his royal retreat in the Highlands with a formal ceremony outside the castle gates on Tuesday.
He was received by a guard of honour provided by Balaklava Company, 5th Battalion The Royal Regiment of Scotland, of which he is the Colonel-in-Chief.
© Getty ImagesThe Prince and Princess of Wales joined the monarch at the royal residence on Thursday, HELLO! revealed, alongside their three children, Prince George, 13, Princess Charlotte, 11, and Prince Louis, eight.
They typically spend part of their summer holiday at Balmoral each year, though it's not known how long their stay will be.
How has the royal family reacted to news of Harry's return?
The King was informed of the news on Sunday and welcomes the opportunity to see more of the family in a private and personal capacity, it is understood.
However, HELLO!'s royal editor Emily Nash says that Prince William and Kate are likely "not delighted" about the news of Harry's imminent return.
She told a special episode of HELLO!'s A Right Royal Podcast, which is out now: "Well, what is intriguing about this is the complete radio silence coming from that end of the spectrum. And what's interesting about it is that they're normally away at this time of year. I imagine they're not delighted about this.
Author Robert Jobson told us that the Prince of Wales must "be feeling slightly aghast" and will be feeling "pressure" to "act in a more pragmatic way".
