The Queen, who turned 96 in April, dressed up for the important royal occasion in a pastel blue outfit, which featured white embroidered detailing.
The coat dress was the same Angela Kelly design that she wore to pose in at Windsor Castle for her official portrait to marking her 70 years on the throne.
For its latest outing, she added a matching hat and a pair of white gloves along with her beloved pearl earrings and triple-layered pearl necklace.
Eagle-eyed viewers might have also spotted the ornate diamond brooch, featuring a small crown, she had pinned to her ensemble.
Known as the Brigade of Guards Brooch, she traditionally wears it to Trooping the Colour every year, and this historic year was no exception.
It combines the badges of the five Household Regiments – the Grenadier, Coldstream, Scots, Irish and Welsh Guards.
Originally created for her grandmother, Queen Mary, in the early twentieth century, the Queen began wearing it herself in 1987 when she stopped wearing uniform to the parade.
Earlier today, the Queen waved to the crowd in from the Buckingham Palace balcony alongside senior members of the Royal Family.
These included her son Prince Charles and his wife Camilla, Duchess of Cornwall, as well as her grandson Prince William, his wife Catherine, Duchess of Cambridge and their three children.
Prince George, Princess Charlotte and Prince Louis made their first appearance all together at Trooping the Colour, with the youngest Cambridge child taking after his father William in a sailor outfit.
Notably absent from the Buckingham Palace balcony were Prince Harry and Meghan Markle, who watched the proceedings from the Major General's office with other members of the Royal Family, with the Duchess of Sussex seen playfully shushing junior royals.
Watch: Royal Family watch Jubilee flypast from Buckingham Palace