According to The Royal Correspondent:
On Saturday, June 13, 2015, Her Majesty Queen Elizabeth II…attended the 2015 Trooping the Colour…
Per the British royal court regarding the history and tradition of Trooping the Colour:
Trooping the Colour is carried out by fully trained and operational troops from the Household Division (Foot Guards and Household Cavalry) on Horse Guards Parade in Whitehall…
This military ceremony dates back to the early eighteenth century or earlier, when the colours (flags) of the battalion were carried (or ‘trooped’) down the ranks so that they could be seen and recognised by the soldiers.
To read the entire article in The Royal Correspondent, please click here.