King Charles lost his temper with a faulty pen during a signing ceremony in Northern Ireland on Tuesday.
The monarch became frustrated after ink spilled out of the fountain pen and onto his hands - after he signed a date wrong on an official document.
The new King was taking part in the signing ceremony at Hillsborough Castle, the royal family's home in Northern Ireland, when he became annoyed.
He is heard asking an aide for the date, only to realise he has written that it was September 12, rather than September 13.
"Oh God, I've put the wrong date down," Charles says.
The Queen Consort, Camilla, then points out that the King signed another document saying it was the 12th earlier in the day.
"Oh God I hate this," Charles responds, rising to his feet and handing the pen to his wife.
"Oh look, it's going everywhere, hang on," Camilla says as ink seeps from the pen and an aide rushes forward to take it from her.
Charles then fumes: "I can't bear this bloody thing! What they do, every stinking time."
Grieving Charles has had a whirlwind of engagements since his mother, the Queen, died on Thursday, aged 96.
He spent most of Tuesday in Northern Ireland, after flying from Edinburgh on Tuesday morning.
The King and the Queen Consort Camilla arrived in Belfast late on Tuesday morning (UK time) and were greeted by the Lord Lieutenant of Belfast, Dame Fionnuala Mary Jay-O'Boyle, and Northern Ireland Secretary Chris Heaton-Harris.
The royal couple then travelled to Hillsborough Castle in County Down, the royal family's only residence in Northern Ireland.
Charles was seen grinning as he greeted children who had gathered outside to meet him, as well-wishers offered flowers.
One royal fan even tried to hand the King a corgi called Connie, in a touching nod to the late Queen's love for her pets.
At the castle, the new King met the nation's political leaders, including senior members of Sinn Fein - the republican party that was closely associated with the IRA during the Troubles and refuses to swear allegiance to the Crown.
At Hillsborough, Charles pledged to follow the "shining example" his mother had set during her "long life of public service".
He told gathered dignitaries that he would "seek the welfare of all the inhabitants of Northern Ireland".
The King then travelled to St Anne's Cathedral in Belfast for a Service of Reflection for the Queen.
On Monday night, Charles and his siblings - Prince Andrew, Princess Anne and Prince Edward - held a vigil over the Queen's coffin at St Giles' Cathedral in Edinburgh.
The Queen's body has now arrived at Buckingham Palace in London where Charles, Camilla and other royals will again gather.
On Wednesday, the royals will follow the Queen's coffin as it carried to Westminster Hall, where her body will lie in state for four days.
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