King Charles III has worn his brand new royal cypher for the very first time. His Majesty was formally proclaimed monarch at the Accession Council on Saturday morning after the death of Queen Elizabeth II on Thursday after a remarkable 70 years on the throne.
The former Prince of Wales automatically became King once his mother passed away but the Accession Council was called as soon as possible to make it official - and he marked the historic occassion by debuting a special symbol that will start to appear on things we use every day such as coins, stamps and postboxes.
For the latest updates as the world mourns the Queen and King Charles III's reign begins, follow our live blog.
Charles' royal cypher, a monogram used by a country's reigning sovereign, was worn on a tie pin when he officially became King at St. James' Palace.
It usually consists of the monarch's initials and title, so the new Kings' features the letters 'CR', which stands for 'Charles Rex III', intertwined with a crown on top.
The 'R' stands for 'rex', which means 'king' in Latin - and His Majesty used the signature 'Charles R' when signing the declaration.
The Queen had the cypher 'ER' but it meant something different, as the 'r' is for the Latin word for 'queen', which is 'regina'.
The tradition of signing with the initial R goes back centuries for English monarchs as far as Henry I in the early 12th century - and is used to designater authority of the sovereign.
There have been exceptions, as Queen Victoria used 'Victoria RI', which stands for 'Rex Imperator', when she became Empress of India.
The royal cypher is now most commonly seen on red post boxes across the country as well as duty stamps.
More than 60% of the UK's 115,000 post boxes carry the royal cypher of the Queen, but in Scotland, they feature the Scottish crown.
Royal Mail post boxes bearing Queen Elizabeth’s royal cypher, EIIR, are unlikely to be removed in the near future, but stamps are expected to change fairly quickly.
Since 1967, all stamps issued by the Royal Mail have featured an embossed silhouette of the side profile of the Queen.
Royal Mail will now stop producing the stamps baring the Queen's silhouette- although they can still be used on letters and parcels - and will begin the process to create new ones.
The new King has featured on stamps before, including on the ones released for his 70th birthday in 2018, but Royal Mail are yet to confirm what the new designs will look like.
The royal cypher can also be found on government papers, government buildings across the Commonwealth, army and navy uniforms and on some of the royal staff's clothes.
All British passports have been issued under the name of Her Majesty and are still valid for travel.
However, new passports, will now be printed with the wording on the inside of the front cover to His Majesty.
There may not be a change to our cash for some time. - and experts expect the public to have a mix of monarchs on their currency.
One thing that will be noticeably different is that consecutive monarch's must face in a different direction, so Chalres' side profile will face the other way.
Today marked the start of an incredibly busy period for the new King, who officially became the monarch today at the Accession Council.
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.
King Charles 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.
On Monday, Charles will receive the motion of condolence at Westminster Hall before starting his UK tour with a visit to the Scottish parliament and a service at St Giles Cathedral in Edinburgh.
Tuesday will see the King arrive in Northern Ireland, where he will receive another motion of condolence at Hillsborough Castle and attend a service at St Anne's Cathedral in Belfast.
He will then travel to Wales on Friday to receive another motion of condolence at the Welsh parliament and attend a service at Llandaff Cathedral in Cardiff.
* 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 poth pullouts.
You can leave your tributes to Queen Elizabeth II here
