Celebration of the Birthday of His Majesty the King

The official birthday tradition was started by George II in 1748. With a November birthday being too cold for a celebratory parade, he tied his celebrations in with the annual Trooping the Colour military parade.

Summer 'official' birthday celebrations were standardised during the reign of Edward VII, who also had a November birthday, according to Royal Museums Greenwich.

Since 1748, the monarch's official birthday has been marked by an outdoor parade known as Trooping the Colour which was usually held on the king or queen's actual birthday. Edward VII, who reigned from 1901 to 1910, was born in November. Instead of making the troops parade on a cold and dark November morning, the tradition began of celebrating his birthday officially in May or June as there was less chance of it being chilly and drizzly during the event. 

The King is the monarch of 15 countries, the United Kingdom and 14 commonwealth realms.