It comes after two videos of the monarch having issues with pens while signing documents during the mourning period for his late mother, Queen Elizabeth II.
The King and his Queen Consort carried out their first public engagement since the Queen’s death in Scotland on Monday (3 October).
While signing a guest book in Dumferline, Fife, Charles appeared to use his own pen before handing it to Camilla and smiling as he remarked: “These things are so temperamental.”
The monarch appeared to refer to a viral video in which he had the misfortune of using a leaky pen while trying to sign a document in Northern Ireland.
Watch: King Charles laughs after woman hands him a pen 'just in case'
He initially wrote the wrong date while signing in front of the cameras, before the pen began to leak.
“Oh god I hate this [pen]!” he said, losing his temper. “I can’t bear this bloody thing, what they do, every stinking time.”
In another video, as he sat down for his first Privy Council meeting, Charles gestured for an ornate pen holder to be removed from his table by an aide.
Following his mishaps, the King was handed a new pen by a well-wisher while greeting members of the public in Cardiff.
The woman who gifted the monarch with the pen said: “Just in case.”
Charles saw the humour in the gift and laughed as he accepted it, prompting the rest of the crowd to clap and join in the laughter.
The King and his wife visited Dumferline to mark the former town becoming a city, after it won its new status as part of the Queen’s platinum jubilee celebrations.
Later in the day, the royal couple hosted a reception at the Palace of Holyroodhouse in Edinburgh to celebrate South Asian communities in Britain, and met hundreds of guests of British Indian, Pakistani, Bangladeshi, Sri Lankan, Nepalese, Bhutanese and Maldivian heritage from across the country.