King Charles III turns 74 today and his first birthday as monarch has been marked by gun salutes, a Changing of the Guard ceremony at Buckingham Palace and special musical performances.
For the first time, gun salutes have been fired across the capital in honour the King on his birthday with the King's Troop Royal Horse Artillery firing 41 volleys from midday at London's Green Park.
The Band of the Scots Guards are also performing Happy Birthday in the Royal Park.
Watch: Rewatch live broadcast of gun salute for the King's 74th birthday in London's Green Park and Portsmouth.
The last time gun salutes were heard across the capital was to pay tribute to Queen Elizabeth.
Gun salutes took place in locations including Cardiff Castle, Edinburgh Castle, Hillsborough Castle, York, Portsmouth and Gibraltar.
What are gun salutes?
Customarily fired, both onshore and at sea, gun salutes are a sign of respect or welcome.
Royal gun salutes follow proud traditions and are fired on special occasions such as anniversaries and birthdays, and in the event of a death, by military personnel from various locations in London and at saluting stations across the UK and abroad as a mark of respect and admiration for the monarch.
Royal salutes are traditionally fired from locations in London, Portsmouth, Colchester, Plymouth and York in England, Edinburgh Castle in Scotland, Cardiff in Wales, Hillsborough Castle in County Down, Northern Ireland and Gibraltar.
Where does the tradition originate from?
The firing of gun salutes is a custom dating to the early days of sail.
Ships, when on goodwill visits to foreign ports, discharged all their guns to seaward on arrival thus indicating to the authorities ashore that they came in peace with empty guns.
In ancient times, even numbers were associated with mourning, therefore the number of these gun salutes was always odd.
This tradition has been carried on until this day.
In London, the honour falls on the King's Troop Royal Horse Artillery in the Royal Parks and the Honourable Artillery Company at the Tower of London.
Watch: 16 Regiment Royal Artillery gunners on firing Platinum Jubilee gun salute.
Who fires the guns?
The honour of firing the salutes falls on the King's Troop Royal Horse Artillery.
Today, the role of the King's Troop is purely ceremonial.
Its important history dates back to 1793 with the formation of the Royal Horse Artillery.
The unit in its current form was created after the Second World War in 1946 by Royal Decree to have 'A Mounted Battery to fire salutes on state occasions, dressed in the traditional style.'
Initially, the Royal Horse Artillery was known as The Riding Troop. King George VI renamed it in his own honour by scratching out the word 'Riding' in the visitor's book and replacing it with 'King's'.