Kate Middleton dazzled in a yellow ensemble by her favourite designers at the Trooping of the Colour celebration.
The Duchess of Cambridge was greeted by cheers from the huge crowd as she joined the parade down Horse Guards Parade in the Mall.
Kate opted for a dress by Alexander McQueen, which she matched with a stylish Philip Treacy hat.
She also wore Bahrain Pear Drop earrings, said to have been borrowed from the Queen.
The 37-year-old mum-of-three looked radiant as she waved and beamed at the crowd during the parade.
Kate was joined by the Duchess of Cornwall and new parents Meghan and Harry, who welcomed their son Archie at a private London hospital on May 6.
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In another horse-drawn carriage was Princess Eugenie and husband Jack Brooksbank, Princess Beatrice and the Duke of Kent.
New mum Meghan wore a dress by Clare Waight Keller and hat by Noel Stewart.
Camilla had also chosen a mainstay designer Bruce Oldfield who had created a bright green dress and coat with white embroidery teamed with a Philip Treacy hat.
Kate joined the royal family for Prince Louis’ first royal engagement, the celebration to mark the official birthday of the British Sovereign.
Most of the royal family have turned out for the event, which sees 1,400 parading soldiers, 200 horses and 400 musicians.
The display, held in celebration of The Queen’s birthday, closes with a fly-past by Britain’s Royal Air Force.
The Queen arrived in a procession full of pomp and pageantry featuring a Sovereign’s Escort from the Household Cavalry, made up of Life Guards and Blues and Royals, in their silver and gold breastplates and plumed helmets.
Kate was seen earlier this week at the Beating Retreat – a display of military music, horsemanship, precision drill, fireworks and pageantry.
The event paid tribute to the 75th anniversary of D-Day by including a composition taken from The Longest Day, a 1962 film depicting the Normandy landings on June 6 1944.
Kate was the only member of the royal family to attend the event, with the Duke of Cambridge marking the anniversary at an event in Staffordshire earlier on Thursday.