On Saturday, June 13, 2015, Her Majesty Queen Elizabeth II and His Royal Highness The Duke of Edinburgh accompanied by Their Royal Highnesses The Prince of Wales and The Duchess of Cornwall, Their Royal Highnesses The Duke and Duchess of Cambridge, His Royal Highness Prince Harry of Wales, His Royal Highness The Duke of York, Their Royal Highnesses Princess Beatrice and Princess Eugenie of York, Her Royal Highness The Princess Royal and Vice-Admiral Sir Timothy Laurence, Their Royal Highnesses The Duke and Duchess of Gloucester attended the 2015 Trooping the Colour held at Horse Guards Parade, Whitehall in London.
After the ceremony members of the royal family including His Royal Highness Prince George of Cambridge, Lady Louise Windsor, James, Viscount Severn appeared on the balcony at Buckingham Palace.
Per the British royal court regarding the history and tradition of Trooping the Colour:
“Although The Queen was born on 21 April, it has long been the tradition to celebrate the Sovereign’s birthday publicly on a day in the summer, when good weather is more likely.
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, watched by members of the Royal Family, invited guests and members of the public.
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.
Since 1748, this parade has also marked the Sovereign’s official birthday. From the reign of Edward VII onwards, the Sovereign has taken the salute in person at Trooping the Colour.
During the ceremony, The Queen is greeted by a Royal salute and carries out an inspection of the troops.
After the massed bands have performed a musical ‘troop’, the escorted Regimental Colour is carried down the ranks.
The Foot Guards and the Household Cavalry then march past Her Majesty, and The King’s Troop, Royal Horse Artillery, rank past.
The Queen rides in a carriage back to Buckingham Palace at the head of her Guards, before taking the salute at the Palace from a dais. The troops then return to barracks.
Her Majesty then joins other members of the Royal Family on the palace balcony for a fly-past by the Royal Air Force.
The Queen has attended Trooping the Colour every year of her reign, except in 1955 when a national rail strike cancelled the event.”