At the moment of the Queen's death, the throne immediately passed to heir Charles, the former Prince of Wales.
However, he had to go through many practical and traditional steps to be crowned king.
What would he be called?
He will be called King Charles III.
This was the first decision of the new king during his reign. He could choose from any of his four names—Charles Philip Arthur George.
He's not the only one facing a change in title.
Prince William, though heir to the throne, does not automatically become Prince of Wales. However, he immediately inherited another title from his father, Duke of Cornwall. His wife, Catherine, would be known as the Duchess of Cornwall.
Charles's wife will also have a new title, her full name being Queen — a term used for a monarch's spouse.
Formal ceremony
Around the first 24 hours after his mother's death, Charles would be officially proclaimed king. This happened at St James's Palace in London, in front of a ceremonial body known as joining the commission.
This is made up of members of the Privy Council – a group of senior MPs, past and present, and peers – as well as a number of senior civil servants, Commonwealth High Commissioners and Mayor of London.
Theoretically, more than 700 people are entitled to participate, but given the short notice time, the actual number may be much smaller. At the last meeting to join the Board in 1952, about 200 people attended.
The king did not traditionally attend.
At the meeting, the Speaker of the Privy Council (currently a Member of the House of Justice Penny Mordaunt) will announce Queen Elizabeth's death and read the proclamation aloud.
The wording of the proclamation could be changed, but traditionally it was a series of prayers and pledges to praise the previous monarch and promise to support the new monarch.
The proclamation was subsequently signed by a number of senior figures, including the Prime Minister, the Archbishop of Canterbury and the Lord Chancellor.
As with all of these rituals, attention will be paid to content that may have been changed, added, or updated as a sign of a new era.
The King's First Declaration
The Enthronement Council meets again— usually a day later — this time, the King will be present with the Privy Council.
At the beginning of British monarchy, there was no "oath of office" like the president of the United States and other heads of state. But the new king made a statement, and in accordance with early 18th-century tradition, he would swear an oath to protect the Church of Scotland.
After the trumpeter's fanfare, a public manifesto will be issued declaring Charles the new king. This will be made by an official known as the King of Arms of the Gard on a balcony above the Abbey of St. James's Palace.
He would shout, "God bless the king," and for the first time since 1952, the national anthem was played as "God bless the king."
Hyde Park, the Tower of London and naval ships will fire salutes, and Edinburgh, Cardiff and Belfast will read the proclamation of Charles as King.
Coronation
When Charles is officially crowned, the symbolic climax of the ascension to the throne will be the coronation. Due to the need for preparation, the coronation is unlikely to take place soon after Charles ascended the throne – Queen Elizabeth succeeded to the throne in February 1952 but was not crowned until June 1953.
Coronations have been held at Westminster Abbey for the past 900 years – William the Conqueror is the first monarch to be crowned here, and Charles will be the 40th.
It is a religious ceremony of the Church of England and is presided over by the Archbishop of Canterbury. At the climax of the ceremony, he put the Crown of St. Edward on Charles's head, a solid gold crown dating back to 1661.
This is the heart of the Tower of London Crown Jewels, worn only by monarchs at coronation (not least because it weighs 2.23 kg).
Unlike royal weddings, coronations are a national occasion – the government pays for it and ultimately decides on the guest list.
There will be music, reading and the ceremony of plastering the new monarch with orange oil, rose oil, cinnamon oil, musk oil and ambergris oil.
The new king will be crowned in full view of everyone. In this elaborate ceremony, he will receive spheres and scepters as symbols of his new role, and the Archbishop of Canterbury will wear a crown of pure gold on his head.
Head of the Commonwealth
Charles has become head of the Commonwealth, an association of 56 independent states and 2.4 billion people. For 14 of these countries, as well as the United Kingdom, the King is the head of state.
These countries are known as Commonwealth countries and include: Australia, Antigua and Barbuda, Bahamas, Belize, Canada, Grenada, Jamaica, Papua New Guinea, Saint Christopher and Nevis, Saint Lucia, Saint Vincent and the Grenadines, New Zealand, Solomon Islands, Tuvalu.