King Charles III signs an oath to uphold the security of the Church in Scotland during the Accession Council at St James's Palace.

Video. King Charles III officially declared UK’s monarch

The UK’s Accession Council, senior politicians, and advisers to the monarch attended a ceremony in St. James’s Palace, which officially declared King Charles III as the country’s monarch.

The UK’s Accession Council, senior politicians, and advisers to the monarch attended a ceremony in St. James’s Palace, which officially declared King Charles III as the country’s monarch.

The event is a constitutional and ceremonial step meant to introduce King Charles III to his country.

Charles III officially became King of the UK when his mother, Queen Elizabeth II, died Thursday.