The King is celebrating his first birthday as monarch as he turns 74, with the British Army leading celebrations in London.
Charles celebrated his 74th anniversary privately on Monday, with the milestone marked by the Band of the Household Cavalry performing Happy Birthday during the Changing of the Guard ceremony at Buckingham Palace.
Gun salutes were fired across the capital in honour of his birthday for the first time, with the King's Troop Royal Horse Artillery firing 41 volleys from midday at London's Green Park.
Immediately afterwards, the Band of the Scots Guards performed Happy Birthday in the park.
The King’s Troop is a mounted ceremonial unit in the British Army that fires salutes on royal anniversaries and major events such as state visits, and provides a gun carriage and a team of black horses for state and military funerals.
Watch: First King's Guard since King Charles III became head of state takes place.
Later, the Honourable Artillery Company fired a 62-gun salute at the Tower of London.
King Charles became King following the death of the Queen on September 8 and he has since had a busy period.
Charles spent the day before his 74th birthday leading the nation in honouring its war dead during the annual Remembrance Sunday service at the Cenotaph.
His floral tribute to the fallen, left at the memorial in Whitehall, featured the words, "In memory of the glorious dead. Charles R".