Charles became King the moment his mother died under the old common law rule that ensures Britain is never without a monarch and “the King never dies”.

Although it may be several months before he is crowned, the formal process of proclaiming him King – the Accession Council – begins almost straight away.

Charles prepares for first nationwide address – follow live updates

Here Sky News takes a closer look at the Accession Council and the part it plays in transitioning to a new monarch.

What is the Accession Council?

The Accession Council is a group made up of Privy Counsellors, Great Officers of State, the Lord Mayor of London, Realm High Commissioners and senior civil servants.

It only convenes on the death of the monarch, which last happened when King George VI died in 1952.

Members meet as soon as is practically possible after the monarch dies, usually within 24 hours, at St James’s Palace in London.

Following the Queen’s death it will take place slightly later, at 10am on Saturday, 10 September, and will be televised for the first time in history.

It oversees the formal proclamation of the heir to the throne becoming King or Queen, and is split into two parts.

According to Sky News royal commentator Alastair Bruce: “The accession council is a constitutional necessity.

“It derives from Saxon times when all the great chiefs of the land would meet and elect from the living descendants of the god King Woden.”

Who are its members?

The Accession Council is largely made up of Privy Counsellors and is chaired by its leader, the Lord President of the Council – currently Penny Mordaunt MP – who is also the Leader of the House of Commons.

The Privy Council has more than 700 members, but with only room for around 150 people in the State Apartments at St James’s Palace, only active members are likely to attend.

Summonses are sent to all Privy Counsellors, however, which include past prime ministers, their ministers and leaders of the opposition.

The Queen Consort and Prince William will both be there as Privy Counsellors, as will Sir Angus Ogilvy, who is married to the Queen’s cousin Alexandra.

The Lord Mayor of London – currently Vincent Keaveny – will also be invited, alongside the High Commissioners or acting High Commissioners of all 14 Commonwealth states.

Scotland’s First Minister, Nicola Sturgeon, and the secretary of state for Scotland are also part of the Accession Council, along with the current Lord Chancellor and the Lord President of the Court of Session.

Part One

The first meeting of the Accession Council takes place without the new King or Queen to formerly proclaim them the new sovereign.

It happens at St James’s Palace – formerly the main London residence of the monarch until it moved to Buckingham Palace in the 1800s.

King George VI died in the “early hours” of 6 February 1952, with the council meeting for the first time 17 hours later. There were 191 council members present.

The meeting begins with the Lord President announcing the death of the monarch and calling upon the Clerk of the Council to read the Accession Proclamation.

The Queen’s proclamation text read: “Whereas it has pleased Almighty God to call to his mercy our late sovereign Lord King George VI of blessed and glorious memory, by whose decease the Crown is solely and rightfully come to the high and mighty Princess Elizabeth Alexandra Mary.

“We, therefore, the Lords Spiritual and Temporal of this Realm, being here assisted with these his late Majesty’s Privy Council, with representatives of other members of the Commonwealth, with other principal gentlemen of quality, with the Lord Mayor, Aldermen, and Citizens of London, do now hereby with one voice and consent of tongue and heart publish and proclaim that the high and mighty Princess Elizabeth Alexandra Mary is now, by the death of our late sovereign of happy memory, become Queen Elizabeth II.

“By the grace of God Queen of this realm and of all her other realms and territories, Head of the Commonwealth, Defender of the Faith, to whom her lieges do acknowledge all faith and constant obedience with hearty and humble affection, beseeching God by whom Kings and Queens do reign, to bless the Royal Princess Elizabeth II with long and happy years to reign over us.”

The proclamation is usually the first time the new monarch’s official title is revealed, but on this occasion, Clarence House has already announced he will go by King Charles III.

After the proclamation text has been read, it is then signed by members of the “platform party”, which include any royals who are Privy Counsellors, the prime minister, Lord Chancellor, Lord Privy Seal, Earl Marshal, and the Archbishops of Canterbury and York.

The Lord President calls for silence and then reads any remaining items of business.

Part Two

The second meeting of the Accession Council is attended by the new monarch and is effectively their first meeting of the Privy Council – as it is only attended by Privy Counsellors.

Traditionally the second part takes place immediately after the first, but as the Queen was abroad when her father died, it took place two days later once she was back in England.

This time it will begin at 11am on Saturday with the King reading a personal declaration about the death of his mother.

The Queen’s read: “By the sudden death of my dear father, I am called to assume the duties and responsibilities of sovereignty.

“At this time of deep sorrow, it is a profound consolation to me to be assured of the sympathy which you and all my peoples feel towards me, to my mother and sister and to the other members of my family.

“My father was our revered and beloved head as he was of the wider family of his subjects. The grief which his loss brings is shared among us all.

“My heart is too full for me to say more to you today than that I shall always work as my father did throughout his reign to uphold constitutional government and to advance the happiness and prosperity of my peoples spread as they are all the world over.

“I know that in my resolve to follow his shining example of service and devotion, I shall be inspired by the loyalty and affection of those whose Queen I have been called to be, and by the counsel of their elected parliaments. I pray that God will help me to discharge worthily this heavy task that has been laid upon me so early in my life.”

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The monarch then reads the Scottish Oath, which has been taken by every King and Queen of England since George I’s accession in 1714.

It dates back to a time when Catholic Europe was seen as an existential threat to Britain and protects the
security of the Church of Scotland – as unlike in England – church and state are separate there.

The Queen’s Scottish oath read: “I, Queen Elizabeth II by the grace of God of the United Kingdom of Great Britain and Northern Ireland and of my other realms and territories King, Defender of the Faith, do faithfully promise and swear that I shall inviolably maintain and preserve the settlement of the true Protestant religion as established by the laws made in Scotland in prosecution of the claim of right and particularly by an act intituled ‘An act for securing the Protestant Religion and Presbyterian Church Government’ and by the acts passed in the parliament of both Kingdoms for Union of the two Kingdoms, together with the government, worship, discipline, rights and privileges of the Church of Scotland. So help me God.”

The monarch then signs two instruments that records their signing of the oath, which are witnessed by the royal members of the Privy Council, the first minister of Scotland, lord advocate of Scotland, secretary of state for Scotland, advocate general for Scotland – if they are a Privy Counsellor – the Lord Chancellor and the Lord President of the Court of Session.

One copy goes to the Court of Session to be recorded in the Books of Sederunt and the other is kept in the Books of the Privy Council.

The Lord President of the Council then goes through any remaining items of business before each counsellor signs the proclamation and leaves.

Traditionally, trumpeters from the Life Guards and drummers from the Coldstream Guards play after the meeting finishes.

The Garter King of Arms, Earl Marshal, officers and sergeants of arms will then gather on the balcony above Friary Court at St James’s Palace and read the proclamation.

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Straight after it will be read at the Royal Exchange in the City of London – in the presence of the Lord Mayor of London.

Subsequent readings will follow in Edinburgh, Cardiff, Belfast and locations across the Commonwealth at 12pm on Sunday.

Flags will be flown at full-mast again from the principal reading of the proclamation until the following ones in the four nations.

They will then return to half-mast as a mark of respect for the Queen.

A record of the entire Accession Council proceedings is published in the London Gazette – the UK’s official public record.