Charles, the Queen’s first born, became king immediately after her death on Thursday, but a historic meeting formally confirmed his role on Saturday during the ceremony at St James’s Palace, says the BBC.
The Accession Council, a body made up of senior politicians, judges and officials, proclaimed him as the monarch in the State Apartments.
Following the proclamation, the King formally announced the death of his “beloved mother, the Queen”.
“The whole world sympathises with me in the irreparable loss we’ve all suffered,” he said.
“My mother gave an example of lifelong love and of selfless service. My mother’s reign was unequalled in its duration, dedication and devotion. Even as we grieve, we give thanks for this most faithful life.
“I am deeply aware of this deep inheritance and of the grave duties and responsibilities which are now passed to me,” the BBC quoted Charles as saying.
He then went on to thank Queen Consort Camilla, saying: “I am profoundly encouraged by the constant support of my beloved wife.”
Also in attendance at the ceremony were Prime Minister Liz Truss, and former premiers Gordon Brown, David Cameron, Boris Johnson and Theresa May, as well as Archbishop Justin Welby and Prince William.
Before Charles was named the King, the death of the Queen was formally announced.
The 200 or so people gathered in the room all then said ‘God save the King’ before documents were signed.
Flags that were lowered in mourning for the late Queen will fly full-mast for a short time.
A wave of further proclamations will take place across the UK until Sunday.