The King has chosen a royal cypher featuring the Tudor Crown in an apparent nod to the reign of his grandfather, George VI.
The cypher, unveiled on Tuesday, will adorn buttons, liveries, military uniforms, passports and postboxes as it is gradually unveiled in the months and years ahead.
Below the crown, the King’s initials CIIIR - for Charles III Rex - are interlinked.
The design marks a shift from the St Edward’s Crown that was used by Queen Elizabeth II and has become part of the national identity.
Instantly recognisable, it is replicated everywhere from government buildings and state documents to police uniforms - and is the only one in living memory for most Britons.
The cypher is the personal property of the King and was selected by His Majesty from a series of 10 designs prepared by the College of Arms, which is responsible for creating and maintaining official registers of coats of arms and pedigrees.
A Scottish version of the cypher features the Scottish Crown and was approved by Lord Lyon King of Arms.
It will be used for the first time on Tuesday, when mail sent from the Royal Household is franked at Buckingham Palace.
While broadly following the same pattern, successive monarchs have each taken their own approach to choosing a cypher.
A stylised version of the St Edward’s Crown was chosen by George II, George III, George IV and later by Elizabeth II.
The crown, which is kept in the Tower of London's Jewel House, is reserved for the act of coronation.
Featuring two dipped arches topped with a jewelled monde and a cross pattee, it is studded with 444 precious and semi-precious stones.
The original was thought to have belonged to Edward the Confessor, who was canonised by the Catholic Church in 1161, but was destroyed after the execution of Charles I in 1649.
The current version was made for the coronation of Charles II in 1661 and used at the coronation of Queen Elizabeth II in 1953.
The Tudor crown was depicted on the cyphers of Edward VII, Edwards VIII, George V and George VI.
Worn by monarchs since the reign of Henry VIII, it features two arches surmounted by an orb.
When Oliver Cromwell abolished the monarchy in 1649 and beheaded Charles I, historians feared the crown was lost forever.
Cromwell had ordered that the crown, weighing 7lb 6oz, be melted down, minted and sold as coins. Its 344 precious stones were sold separately while other parts of the crown were passed on intact.
The centrepiece was found under a tree by an amateur detectorist in 2017, ending a 400-year mystery over its whereabouts.
The 2.5in-high, inch-wide solid gold figurine, one of five on the Tudor crown, is now at the British Museum and could be worth £2million, according to historians.
The “R” for Rex or Regina was added to a monarch’s cypher from the reign of Henry VIII.
The design chosen by King Charles is markedly similar to the one chosen by his grandfather.
In a nod to his royal lineage, the King wore a tie pin bearing George VI’s cypher when he was formally proclaimed monarch at his Accession Council and again when he addressed MPs and peers at Westminster Hall, pledging to follow his mother’s example of "selfless duty".
He was later spotted wearing cufflinks bearing the cypher of his great-grandfather, King George V, as he waved to crowds at Buckingham Palace.
The decision to replace cyphers will be at the discretion of individual organisations, and the process will be gradual.
However, the cyphers featured on the gold coats of State Trumpeters and the front of house curtain at the Royal Opera House are expected to be changed imminently.
The cypher is perhaps most regularly seen on postboxes across the UK, which can be used to date the time of their creation.
When a sovereign dies, postboxes are not replaced but any new ones introduced from this point on will feature the King’s cypher.
In Scotland, postboxes do not feature the late Queen’s EIIR cypher because some do not accept that she was the second monarch of that name, as Queen Elizabeth I was not a ruler of Scotland.
Earlier postboxes bearing the cypher were vandalised and even blown up, according to the postal museum, and as a result now depict the Scottish crown.