Charles has become King Charles III – with his title as monarch a personal choice that was entirely his own.
He has opted to use his Christian name, just like his late beloved mother Queen Elizabeth II.
The new monarch could have followed royal tradition for many kings and picked George, becoming George VII.
There had been speculation in the past that Charles favoured George VII for historical reasons and because of his devotion to his grandmother, the Queen Mother, and her love for her husband, George VI.
However, after spending decades as Charles, the new king has chosen his own name, just as his mother did.
A new monarch’s name is traditionally announced at the historic Accession Council, which takes place as soon as possible at St James’s Palace in London in the days after the death of a sovereign.
It forms part of the proclamation of the new king.
But Prime Minister Liz Truss referred to King Charles III in her speech outside Downing Street, saying: “Today the Crown passes, as it has done for more than a thousand years, to our new monarch, our new head of state, His Majesty King Charles III.”
Clarence House confirmed the title.
There has been a tradition over the last century for the regnal title to be different from the sovereign’s Christian name.
Queen Victoria’s name was actually Alexandrina Victoria, while Edward VII was born Albert Edward and known as “Bertie”. George V used his given name George.
Edward VIII, who abdicated, had Edward as a first name but was always known to friends and family as David, the last of his seven forenames.
Charles’s grandfather, George VI, was christened Albert and was also known as “Bertie”, but chose his fourth forename, George, to rule under as head of state.
When Princess Elizabeth acceded the throne on the death of her father, she was asked what name she wished to use as queen.
She is said to have replied: “My own name, of course. What else?”
In 1953, there was an unsuccessful legal challenge by John MacCormick, the rector of the University of Glasgow, who disputed the right of Queen Elizabeth II to style herself “the Second” when Elizabeth I had been queen of England, but not of Scotland.
But it was determined that the choice of regnal number is down to royal prerogative.
Charles could have decided to choose from one of his four Christian names. He was christened Charles Philip Arthur George.
After the House of Hanover came to power in 1714, Georges – from George I to George IV – ruled for 116 years in a row.
Picking Charles, however, maintains continuity and fortifies the Charles “brand”.
The name Charles – which comes from the Old German word karl, meaning “free man” – is seen as historically jinxed by some in royal circles.
Charles I was the only British monarch to have been publicly tried and executed for treason, while Charles II – known as the Merry Monarch – spent many years in exile, had 13 illegitimate children and numerous mistresses including Nell Gwyn.
His reign also featured the plague and the Great Fire of London.
Although Charles is Charles III, Bonnie Prince Charlie – The Young Pretender – was known to his supporters as Charles III.