Charles has officially been proclaimed King during a meeting of today's historic Accession Council following the death of his mother the Queen.
After giving a speech to those assembled, he sat down to sign official declarations with his pens lined up on an ornate tray that had been placed on the table. However, there appeared to be an awkward moment when the tray got in the King's way as he went to sign the documents - and it seemed he ordered it for it to be taken away. Charles grimaced and pushed the tray before somebody was hand to remove it from the table so he could carrying on with his signing duties.
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The moment was picked up by many on Twitter with one remarking: "The King not very happy that the pen tray was in his way."
Another noticed: "I think the king didn't want that pen tray there."
While another said: "King Charles really grumpy at the pen tray left on the table."
Meanwhile it emerged that an ink pot placed on the table was of significance to the King - it was actually a gift from his two sons Prince William - the new Prince of Wales - and Prince Harry.
Today's Accession Council was televised for the first time ever, with Queen Elizabeth II's happening behind closed doors 70 years ago, which gave us incredible insight into the formal process.
The new King followed a tradition going back centuries by signing the declaration with 'Charles R' - but he added the letter for a different reason to his late mother.
The Queen used the signature 'Elizabeth R' on official documents - but it's not to represent a secret name.
It actually stands for 'regina', which means 'queen' in Latin - and because Charles is King, his 'R' stands for 'rex'.
The tradition of signing with the initial R goes back centuries for English monarchs and is used to designater authority of the sovereign.
It goes back as far as Henry I, who ruled in the early 12th century, and is how all official documents and formal letters are signed.
More than 200 privy councillors, made up of mostly senior politicians past and present including former prime ministers, were present to hear the Clerk of the Council read the proclamation.
He made a personal declaration on the death of the Queen saying: "I know how deeply you and the entire nation, and I think I may say the whole world, sympathise with me in this irreparable loss we have all suffered.
"Her reign was unequalled in its duration, its dedication and its devotion. Even as we grieve, we give thanks for this most faithful life."
A wave of national transformation is now in full swing as once-in-a-generation procedures that have been decades in the planning are put into action. His Majesty will be meeting many powerful figures today as he is holding audiences at Buckingham Palace.
You can leave your tributes to Queen Elizabeth II here.
This weekend, the Daily Mirror and Sunday Mirror celebrate the life of Her Majesty the Queen with a commemorative special filled with all the key moments from Britain’s longest reigning monarch. Be sure to pick up your copy of the Daily Mirror and Sunday Mirror to get both pullouts.
