Charles III has been officially declared King and new monarch of the UK at the St James's Palace in London, as the Accession Council signed the proclamation of the new King alongside the Royal Family members, including Prince William and the Queen Consort, as well as senior politicians and the Archbishop of Canterbury. 

Buckingham Palace announced that Queen Elizabeth II Thursday evening, who was the longest-reigning monarch after remaining on the throne for over 70 years, died at Balmoral castle in Scotland at the age of 96, thus automatically promoting Prince Charles as the new king of the United Kingdom immediately. 

Following traditions, the official ceremony took place on Saturday, just three days after her passing, at the St James's Palace in London. The procedure was delayed as the death of Queen Elizabeth II was announced late on Thursday. 

Her death came after crowds gathered outside the Buckingham Palace residence in London as concerns about her health were growing. As many as 100 people stood, while senior royals rushed to Balmoral in Scotland, where the Queen was being treated. 

Newly pronounced King Charles pledged to give lifelong service to the people of the UK and his other realms in a solemn address to the nation a day after the death of his mother Queen Elizabeth II, and is now the head of state of the UK and 14 other realms including Australia, Canada, Jamaica, New Zealand, and Papua New Guinea.

He previously announced that the late Queen Elizabeth II will be mourned from Friday until seven days after her funeral with the exact date of her burial yet to be determined.