The King’s new cypher has been officially revealed as the gradual process of putting the monogram on government buildings, state documents and post boxes begins.
It comes as the royal period of mourning comes to an end, seven days after Queen Elizabeth II's funeral, with the family ready to return to regular duties.
The new monogram - the official stamp of the UK's reigning monarch - is just one of many aspects of life in Britain that will change now the country has a new head of state.
The King's new cypher features his initial, C, with the letter R for Rex - Latin for King - with an intertwined III and a crown above the letters.
It is Charles' personal property and was selected by the monarch from a series of designs prepared by the College of Arms. The symbol will be used by government departments and by the Royal Household for franking mail and the decision to replace cyphers will be at the discretion of individual organisations.
The process will be a gradual one and in some instances the cyphers of previous monarchs can still be seen on public buildings and street furniture, especially post boxes.
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The College of Arms, which designed the cyphers, was founded in 1484 and is responsible for creating and maintaining official registers of coats of arms and pedigrees.
The heralds who make up the College are members of the Royal Household and act under Crown authority.
A Scottish version of the monogram, featuring the Scottish Crown, was approved by Lord Lyon King of Arms.
A Cabinet Office spokesperson said of replacing the late Queen’s cypher with the Charles’ monogram: “Where changes can be made easily, such as digital branding, they can be made immediately.
“Physical items such as signage or stationery will be replaced gradually over time as the need arises.”
Since the death of the Queen on September 8, the Royal Family has only carried out official duties where appropriate, and its members have dressed in black as a mark of respect when in public. From Tuesday they will be able to carry out their normal official roles in full after observing the seven-day period of mourning.
Charles carried out one official engagement during royal mourning, holding a telephone audience with the Chancellor Kwasi Kwarteng on Thursday evening, the eve of his tax-cutting mini budget. The Prince and Princess of Wales praised volunteers and operational staff they met at Windsor that day, for their efforts at events surrounding the Queen’s committal service. The King travelled to Scotland soon after the Queen’s funeral last Monday and could remain at his home of Birkhall into early October, following the tradition set by the late monarch. The Queen would normally spend around 10 weeks at her Scottish home during summer, returning to London around the time the autumn session of Parliament began. Planning is already likely to be under way for the King's coronation, but earlier on Monday the Duke of Norfolk, 65, who organised the Queen’s funeral and will stage the crowning of the King, was banned from driving for six months after pleading guilty to using his mobile phone behind the wheel.
He received the punishment despite claiming he needed his licence to arrange the upcoming coronation. The Queen waited over a year for her coronation ceremony which was staged on June 2 1953, after her father King George VI died on February 6 1952.