She left Buckingham Palace in a horse-drawn carriage and sat next to her husband, Prince Harry, Catherine, Duchess of Cambridge, and Camilla, Duchess of Cornwall.
Wearing a blue hat, the Duchess of Sussex waved to thousands of people gathered in the mall in London to watch the spectacle of more than 200 horses, 400 musicians, and 1,400 officers.
The monarch is technically the head of the British forces and would traditionally lead an army to war. The parade, which gives the queen the opportunity to check her army, moves down the mall from Buckingham Palace to the Horse Guard's parade. Members of the royal family travel on horseback or by coach.
When the queen was younger, she would ride saddle on horseback to greet the public. But in recent years she travels by horse and carriage.
That year, the queen was whipped into cream as she drove with a state carriage from Buckingham Palace to the parade of the Horse Guard.
It was followed by Charles, the Prince of Wales, the Duke of York, the Duke of Cambridge and their daughter, the Princess Royal, who were all on horseback.
The Queen inspects the troops at the Horse Guard's parade before returning to Buckingham Palace at the head of their guards. In the palace, the entire royal family gathers on the balcony to watch the colorful flyby of the Royal Air Force.
The event will also feature a 41-gun salute at Green Park by the Horse Artillery.
The Queen's birthday is on April 21st. However, official festivities always take place in June, often for a whole weekend. The nation's longest reigning monarch turned 93 in April.
A Family Affair
Although the Duchess is still on maternity leave, a royal source told CNN that this is a family moment in which many members of the royal family will be present.
According to the source of the palace, this is a different matter from the official duties of the Duchess to attend an official state visit.
Catherine, the Duchess of Cambridge, also participated in an earlier Trooping the Color during her maternity leave but no official tasks.
Angela Dewan of CNN contributed to this report.