Charles took part in the famous Trooping the Colour event where military pomp and pageantry were on display in the heart of London.
The Princess of Wales and her children joined the Queen and thousands of spectators at Horse Guards Parade in Whitehall to view the spectacle featuring some of the UK's most prestigious regiments.
Trooping the Colour is as much a social occasion as a ceremonial event and stands around Horse Guards Parade were filled with about 8000 family members of the guards and officers on parade.
Crowds gathered in The Mall to watch the royal family's carriage procession from Buckingham Palace with Charles and Camilla in the middle of a Sovereign's Escort provided by the Household Cavalry Mounted Regiment.
Riding behind the King were the royal colonels - the Prince of Wales, who is Colonel of the Welsh Guards; the Princess Royal, Colonel of the Blues and Royals; and the Duke of Edinburgh as Colonel of the Scots Guards.
The way was led by the Band of the Household Cavalry with two shirehorses bearing solid silver kettle drums and musicians.
The route was lined for the first time by personnel from all three military services, including units from the 1st Battalion Coldstream Guards to the 26 Engineer Regiment, 16th and 4th Regiments Royal Artillery, the Royal Lancers, the RAF Regiment and the Royal Navy.
The King's first duty was to inspect the troops and he was followed by the royal colonels William, Anne and Edward as he travelled in a carriage past service personnel with the Queen.
In centuries past, colours - or flags - were carried or "trooped" down the ranks so soldiers would recognise them on the battlefield.
In the 18th century, guards from the royal palaces assembled daily on Horse Guards to "troop the colours" and it was around that time that it was decided the parade would also mark the sovereign's official birthday.
The King's actual birthday is on November 14, when he will turn 78.
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