At a ceremony held at St. James's Palace, Charles III was crowned king.
After his mother Queen Elizabeth II passed away, Charles immediately ascended to the throne, but a historic gathering on Saturday formally recognised him in that capacity.
Although it is unknown when the Queen would pass away, the King gave his approval for the day of her funeral to become a bank holiday during the Accession Council.
The momentous event is being shown on television for the first time.
The Privy Council, a body of prominent politicians who advise the monarch, met for the first time during the second portion of the event even though the King himself was initially absent.
Before saying "God Save the King," Clerk of the Privy Council Richard Tilbrook referred to Charles as "King, ruler of the Commonwealth, and protector of the religion."
Senior politicians, judges, and government representatives crowded inside the State Apartments of the Palace in London repeated the sentence aloud.
The King announced that it was his "most painful duty" to inform the public of his mother's passing.
He said: “I know how deeply you, the entire nation, and I think I may say the whole world, sympathise with me in the irreparable loss we’ve all suffered.
“It is the greatest consolation to me to know the sympathy expressed by so many to my sister and brothers.”
The ceremony was attended by 200 members of the Privy Council, including former Prime Ministers Boris Johnson, Theresa May, David Cameron, Gordon Brown, Tony Blair and John Major.
Later, applause and cheers of “God Save the King” broke outside St James’s Palace, before a crowd of thousands sang the national anthem.
It was the decision of King Charles III to allow television cameras into the Accession Council for the first time to allow the public to view proceedings.