Charles, then pictured as Prince of Wales (right) by the The Imperial State Crown in the House of Lords Chamber, in the Houses of Parliament, in London, on May 10, 2022. Photo: Ben Stansall / POOL / AFP
Queen Elizabeth II's eldest son Charles became King as soon as his mother died.
King Charles III made his first statement as monarch half an hour after the Queen's death.
However, declarations and proclamations are still needed in the coming days to formalise his accession to the throne.
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How does accession happen?
As outlined by the Privy Council UK, accession is the event of a new sovereign - in this case Charles - coming to the throne upon the death of their predecessor.
This is where the Accession Council comes in.
The council includes privy counsellors - essentially, advisers to the sovereign - as well as high commissioners, senior civil servants, the Lord Mayor of the City of London and other figures.
The meeting is customarily held at St James's Palace in London.
The Privy Council is yet to announce the official time of the council's meeting but has sent out email invitations to those summoned to attend.
What happens at St James's Palace?
The proclamation of Charles as King will happen at 9am on Saturday, UK time (8pm NZT) in the State Apartments of St James's Palace in London.
About 700 people could be invited to attend the ceremony.
However, given the short notice the number is likely to be much lower.
At Queen Elizabeth II's ceremony on 8 February, 1952, there were fewer than 200 people in attendance.
The Lord President of the Privy Council, Penny Mordaunt, is also leader of the House of Commons.
When the meeting begins she will announce the death of Queen Elizabeth II and call upon the Clerk of the Council to read aloud the Accession Proclamation.
Police officers march past Friary Court at St James's Palace in London a day after Queen Elizabeth II died. Photo: Niklas Halle'n / AFP
The proclamation is then signed by senior figures including present members of the royal family, the British Prime Minister and the archbishops of Canterbury and York.
The proclamation will then be read from the Proclamation Gallery, a balcony above the Friary Court of St James's Palace, by the Garter King of Arms, currently David White.
He will be accompanied by the Earl Marshal and other officials wearing traditional heraldic clothing.
The proclamation will be accompanied by gun salutes.
Heralds will travel to Mansion House in the City of London, where the proclamation will be read at the Royal Exchange.
The proclamation will also be read publicly in Edinburgh, Belfast, and Cardiff.
In New Zealand, a proclamation of accession ceremony will be held in Parliament Grounds at 12.30pm tomorrow.
Then there is a second part
King Charles III is then expected to attend his first Privy Council meeting as monarch.
When he enters the room business begins with King Charles's personal declaration relating to the death of the Queen.
Next, he will take the oath that unites the churches of England and Scotland, known as the accession declaration - a tradition since King George I in 1714.
This second ceremony does not always follow part one straight away.
Following the death of King George VI during the early hours of 6 February, 1952, part one of the Accession Council for Queen Elizabeth II was held at 5pm the same day.
The second part had to wait until the Queen got back from Kenya two days later.
What about the coronation of King Charles III?
Queen Elizabeth II poses on her Coronation day Photo: AFP
It may be more than a year before Charles's coronation.
The coronation is a formal ceremony in which Charles will be physically crowned King.
Traditionally coronations are held at Westminster Abbey.
Queen Elizabeth II's coronation was on 2 June, 1953, 16 months after her father's death.
-ABC / RNZ