The royal colonels, all on horseback, will accompany the Queen, Prince Charles, Princess Anne and Prince William. Since 1748, Trooping the Colour has been the official commemoration of the sovereign's birthday, and throughout her reign, the Queen has never missed the occasion, apart from in 1955 when the event was cancelled due to a national rail strike.
On Saturday, Meghan was pictured wearing a pale pink dress with matching hat, while Harry was in military uniform.
This year, the newest addition to the ceremony was, of course, the Duchess of Sussex Meghan Markle.
While also taking part was the King's Troop Royal Horse Artillery, who will fire a 41-gun salute in Green Park to mark the Queen's official birthday.
All eyes were on newly-weds Prince Harry and his wife Meghan, who made their first appearance together since apparently slipping away for their honeymoon last week.More news: Merkel hand Macron olive branch on eurozone reforms
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The day's proceedings closed with an RAF flypast, which was watched by members of the royal family from Buckingham Palace's balcony.
George, who turns five in July, was just as excited as he watched the roaring fly-past by the Royal Air Force.
Meghan fussed with her loose hair and seemed to be troubled by her Philip Treacy hat.
The Duchess added a pair of drop earrings to her reliably chic wardrobe choice and teamed it with one of her timeless staples - heeled court shoes. She was also spotted covering his mouth with her hands.
All the royals travel in different carriages and make their way up to the balcony where they greet the audience.
Meghan's remarkable confidence at the event reminds us of when Catherine, Duchess of Cambridge's made her Trooping of the Colour debut less than two months after her April 2011 nuptials to Prince William. Meghan and Harry have stated their desire to jump right in and get to work in their new roles.