In the 18th century, guards from the royal palaces assembled daily on Horse Guards to "troop the colours" and in 1748 it was announced that the parade would also mark the Sovereign's official birthday.
She rode with her husband Prince Philip in an open carriage in the procession along Horse Guards Parade.
A Buckingham Palace spokeswoman said the Countess of Wessex did not attend as she had a private engagement.
The centerpiece of London's highbrow season of festivities, the celebration takes place in June in hopes of favorable weather despite the fact that her Her Majesty's actual birth date is April 21. However, both the royal children handled themselves like seasoned pros, waving to the crowds from the balcony and staring up in awe as the Royal Air Force flew overhead.
In other words, we needed a Prince George and Princess Charlotte sighting more than ever.
It was Prince George's third appearance at the annual Trooping the Colour parade and Princess Charlotte's second, and they appeared with the Duke and Duchess of Cambridge during the Royal Airforce flyover. Charlotte looked darling twinning with mom Kate in a bubble gum pink dress while George looked dashing in his tiny suspenders.
Tens of thousands of people lined the streets to watch the spectacular parade, on a glorious summer's day in London.
Prince Charles, Prince William and Princess Anne arrived on horseback.
An excited Prince George and Princess Charlotte could be seen peering out of the Buckingham Palace balcony window before joining great grandmother - "Gan Gan" - and the rest of the royal family on the balcony.
The Trooping of Colour parade on Saturday morning was marked with a minute's silence to honour the victims of the Grenfell Tower fire in London, along with those who died in the recent terror attacks in London and Manchester.