Charles III was officially proclaimed the new king of the United Kingdom and 14 Commonwealth countries at a ceremony at St James's Palace in London on Saturday. The Prince of Wales succeeds Elizabeth II, who died on Thursday at the age of 96 at Balmoral Castle in Scotland, her summer residence.
The ceremonial Ascension Council declared Prince Charles Philip Arthur George as the new monarch Charles III, after which those attending the ceremony, especially political figures such as former prime ministers Boris Johnson, Theresa May, David Cameron, Gordon Brown and Tony Blair, shouted "God save the king".
Although the heir succeeded his mother automatically after her death, this is the traditional event at which the British political establishment officially recognises him as sovereign.
After announcing the Queen's death and proclaiming her successor, the newly appointed President of the Council, Penny Mordaunt, ordered the members of the Privy Council, a small group of political and social authorities who advise the monarch, into a separate room. Among others, the Prime Minister, Liz Truss, and the Prince of Wales, William, are in the room.
The heir to the throne said he would follow "the example" of his mother, Elizabeth II, and said he was "deeply conscious" of his legacy and "the duties and vast responsibilities of sovereignty" he had inherited.
Charles III has also pledged to respect constitutional principles and to serve the citizens with dedication during his reign. In his statement, he reiterated, as in Friday's message to the nation, the enormous regret felt by his family and the entire country at the death of his mother, whose reign was unprecedented in "duration, dedication and devotion".
"It is a great comfort to me the sympathy expressed by so many for my sister and brothers and may all this overwhelming affection and support be extended to the whole family in our bereavement," the king said in a formal, restrained tone.
At the end of his address to a large group of political and social authorities, Charles III also swore an oath to ensure the protection of the Church of Scotland - he is head of the Anglican Church - and authorised the distribution of his declaration to be read out in Scotland, Wales and Northern Ireland, as well as in the countries that make up the Commonwealth.
"In assuming these responsibilities, I will strive to follow the inspiring example that has been given to me in upholding constitutional government and seeking peace, harmony and prosperity for the peoples of these islands and Commonwealth realms and territories throughout the world," he said.
He then sat down to sign a document certifying that he had taken the oath, in the presence of Queen Consort Camilla and Prince William of Wales.
The King, who has no political power in principle, said he would be guided by the respective parliaments and said he was confident he would have the support and affection of the public. He also confirmed that he would continue the current practice of handing over inherited income to the public purse, which is then used to subsidise the Royal Family in their official activity.
"In order to carry out the heavy task that has been entrusted to me, to which I dedicate the rest of my life, I pray for the guidance and help of Almighty God," he concluded.
This is the first official act of Charles III as head of state that is unrelated to the coronation ceremony, with great pomp and pageantry, which is expected to take place in the coming months.