The former Prince of Wales became king at the age of 73, following the death of his mother, The Queen, at 96 years old.
King Charles III was joined by his wife Queen Camilla, and his son Prince William, The Duke of Cornwall and Cambridge at the Queen’s residence in Balmoral, on September 8.
In a statement, King Charles III said: “We mourn profoundly the passing of a cherished Sovereign and a much-loved Mother.
“I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world.”
He added: “The death of my beloved mother, Her Majesty The Queen, is a moment of the greatest sadness for me and all members of my family.”
When will Prince Charles be crowned King and when is the King’s first declaration?
The formal proclamation of King Charles III to be televised in TV first with the Accession Council being televised for the first time in history, Clarence House has confirmed.
Buckingham Palace earlier announced that the council would officially proclaim King Charles III in the state apartments of St James’s Palace at 10am on Saturday.
The council is made up of members of the Privy Council - a group of senior MPs, past and present, and peers - as well as some senior civil servants, Commonwealth high commissioners, and the Lord Mayor of London.
Although Charles is already king, his coronation may not happen for a few months.
Queen Elizabeth II’s coronation took place on June 2, 1953, more than a year after she became Queen, on February 6, 1952.
According to the BBC, there is no “swearing in” at the start of a British monarch’s reign, but there is a declaration made by the new King and - in line with a tradition dating from the early 18th Century - he will make an oath to preserve the Church of Scotland.
After a public proclamation will be made declaring Charles as the new King. This will be made from a balcony above Friary Court in St James’s Palace, by an official known as the Garter King of Arms.
What will Charles be called as king?
Charles is no longer the Prince of Wales, but King Charles III of England.
On Thursday evening, Prime Minister Liz Truss referred to Charles, the new King, as King Charles III, saying: “Today the Crown passes, as it has done for more than a thousand years, to our new monarch, our new head of state, his majesty King Charles III.”