King Charles III, known for his composed public demeanor, has a less tranquil side that emerges behind closed doors, according to sources familiar with his temperamental outbursts. These episodes have sparked both amusement and concern, offering a rare glimpse into the pressures and expectations placed on the British monarch.

In a notable incident in September 2022, shortly after ascending the throne following Queen Elizabeth II's death, Charles was caught on camera struggling with a leaking pen while signing the visitors' book at Hillsborough Castle in Northern Ireland. "Oh God, I hate this!" he exclaimed, handing the troublesome pen to his wife, Queen Camilla. "I can't bear this bloody thing! What they do... every stinking time!" The incident quickly went viral, casting a spotlight on the king's fiery temper.

Not long after, during the formal Accession Council ceremony, Charles was seen gesturing with irritation over the awkward placement of a pen and its holder. These episodes were not isolated; they revealed a deeper pattern of irascibility that has been corroborated by various sources and former employees.

"Anything he perceives as incompetence particularly brings it out," a former employee told The Daily Beast. "He doesn't suffer fools gladly. In fairness to him, as anyone who has actually worked with him will tell you, he himself is always extremely well prepared, well-read on the subject matter of people he meets and is working with, diligent and respectful of expertise."

This meticulousness and high expectation can sometimes lead to blunt reprimands. "He expects other people to show him the same respect; he can certainly go off at the staff in pretty blunt terms when he perceives someone has not done their job properly, or is just being, to use one of his preferred terms, 'idiotic,'" the source added.

Despite these temperamental outbursts, those close to Charles describe him as a demanding yet ultimately fair boss. "Ultimately, people like working for him, but everyone is under a lot of pressure because his office is incredibly busy. He's absolutely not a monster in the office, but he is human, and he snaps sometimes. Unfortunately, there is sometimes a camera on him when it happens," the former employee noted.

A friend of Charles and Camilla also commented on his temper, noting that it has mellowed over time. "He has an irascible streak to be sure, but it is much better since he has been with Camilla. Everyone, regardless of their position or status, experiences everyday irritations, but literally every move, every gesture he makes is scrutinized."

The scrutiny of his every move is compounded by the inherent pressures of his role. Charles' temper is often compared to that of his relatives. "A tendency towards temper tantrums runs through the Windsors. Philip had it, Charles has it, William has it, and Harry has it. You wouldn't believe what used to come out of William's mouth when he was playing football!" a family friend shared.

Royal biographer Penny Junor, who has written extensively about Charles, described his temper as "fearsome." In her book, "The Firm," Junor noted that Charles can be difficult to advise due to his preference for agreement over impartial advice. Another biographer, Christopher Andersen, recounted an incident where Charles became so enraged at a stuck window while on vacation in the South of France that he threw a chair through it and smashed another window.

Paul Burrell, a former butler to Princess Diana, provided more detailed anecdotes about Charles' particular demands and his reaction when they weren't met. In his book "A Royal Duty," Burrell described how Charles would send handwritten notes to staff with specific instructions, including how he liked his breakfast tray arranged and his preferences for the temperature of his bath. "His underwear is folded in a certain way and his bath towel has to be placed in a certain fashion. When it comes to bathing, the bath plug has to be in a certain position, the water temperature has to be just tepid, and only half full. If anyone gets anything wrong, everybody is scolded," Burrell wrote.

Ken Stronach, a former valet, gave an interview detailing Charles' temper tantrums, including an incident where Charles allegedly grabbed him by the throat after a cufflink was dropped down a sink. Stronach described hiding in a linen cupboard until Charles calmed down.

Facing public scrutiny and personal health challenges, Charles' temperament has reportedly softened. Andersen suggests that facing one's mortality can put things in perspective. "Facing one's mortality obviously puts things in perspective. Things like lost cufflinks and having to wait a few extra seconds for a pen seem less important."

The Daily Beast and OK magazine contributed to this report.