As the King greeted well-wishers in Cardiff, one of them gave him the pen and said "just in case" he experiences any future pen problems.
It appeared the gift went down a treat with the King who saw the funny side of the moment as he accepted the pen while having a chuckle and went on to greet more people in the crowd in the Welsh capital as part of a tour around the devolved nations.
"Oh god I hate this (pen)!" Charles said, standing up from his chair and handing the pen to Camilla. "I can't bear this bloody thing... every stinking time."
This incident divided viewers on social media with one calling him a "spoiled man child" while others were sympathetic to the recent loss of his mother, the Queen.
A clip of the king receiving a new pen from a Welsh well-wisher shared by Sky News has since gone viral, receiving over 3.5m views, 207,000 likes and plenty of comments from people who were amused by the gesture.
King Charles III is handed a pen “just in case” during his visit to Wales
One person wrote: "He's [King Charles] a good sport."
"Good to see him laugh. He had a moment, he’s grieving, it’s honestly understandable even if embarrassing. At least he can laugh now," another person said.
Someone else added: "It’s nice to see him being able to laugh about it."
"I don't think he knew how viral his reaction went," a fourth person replied.
The person claiming to be the pen gift-giver, Kaz Healy, commented: "Highlight of my day!! I MADE THE KING LAUGH!! He took it so well, cracking sense of humour!! Was a pleasure to meet you King Charles."