Strong winds did not stop Kate looking radiant at the Trooping the Colour parade as her hat nearly blew away.
Arriving in a horse-drawn carriage with Prince Harry and the Duchess of Cornwall, the Duchess of Cambridge wore a stunning Jane Corbett hat which matched her silver-grey Erdem dress as she waved to the crowds on the Mall.
The heavy winds in London did not damper the spirits as thousands gathered to watch the Queen's official birthday celebrations.
Cheers: Kate looked stunning in a hat by British-based milliner Jane Corbett and a silver-grey Erdem dress
Only last month Kate wore a pale pink hat by Jane Corbett to a garden party at Buckingham Palace as part of the Jubilee celebrations. The British-based milliner is clearly a favourite.
Kate also wowed the crowds in her embellished dress by Canadian designer Erdem. She proudly watched the Duke of Cambridge, who rode on horseback in his role as Colonel of the Irish Guards.
The Prince of Wales, who is Colonel of the Welsh Guards, the Princess Royal, Colonel of the Blues and Royals, and the Duke of Kent, Colonel of the Scots Guards, were also on parade.
Among the guests were the Duke of York with his daughters, Beatrice and Eugenie, the Earl and Countess of Wessex, Prime Minister David Cameron and wife Samantha, and King Abdullah II of Jordan.
Smiles: Kate travelled to the Horseguards Parade with Prince Harry and the Duchess of Cornwall
Some 1,600 officers and soldiers in the traditional uniforms of the Household Cavalry, Royal Horse Artillery and Foot Guards took part in the parade, with more than 200 horses and around 290 musicians from 10 bands and corps of drums.
The Colour paraded was the flag of the 1st Battalion Coldstream Guards, led by Major Mark Lewis.
After the ceremony, the King's Troop Royal Horse Artillery fired a gun salute in Green Park to mark the Queen's official birthday, while the Honourable Artillery Company fired a 62-round gun salute from the Tower of London.
The royal family rounded off the day's proceedings by gathering on the balcony of Buckingham Palace to watch the traditional RAF flypast.
Chic: Last month Kate wore another Jane Corbett hat to a Jubilee garden party at Buckingham Palace
The Queen celebrated her actual birthday on April 21, when she turned 86, but today's ceremony marked her official birthday, which is always in June.
She first took the royal salute in 1951, when she deputised for her sick father, George VI, and has continued receiving the mark of respect every year, except in 1955, when there was a national rail strike.
The Duke of Edinburgh appeared in good spirits today as he joined the other royals in his first major public engagement since leaving hospital.
Philip attended the traditional display of pomp and pageantry to celebrate the Queen's official birthday after being discharged from hospital a week ago following treatment for a bladder infection.
The Duke showed he is making a good recovery as he waved to the crowds while accompanying the Queen in a glass coach to the televised military spectacle, which is held annually at Horse Guards Parade in Whitehall, central London.
The couple were due to travel in Queen Victoria's 1842 ivory-mounted phaeton carriage but switched due to the 'unpredictable nature of the weather', a Buckingham Palace spokesman said.
Some of the biggest crowds ever to watch the procession lined the Mall, while thousands of people packed into seats and stands to see precision marching by hundreds of Guardsmen.
The Queen, wearing a primrose yellow coat and dress by Angela Kelly with matching hat, and displaying her Brigade of Guards brooch, stood beside the Duke as they inspected the long line of troops wearing their red tunics and bearskins.
The Duke of Edinburgh joined the other royals on the balcony in his first appearance since being hospitalised
Thousands gathered on the Mall to celebrate the Queen's official birthday
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