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Having set out in a horsedrawn carriage procession from Windsor Castle, the monarch was greeted by cheers and shouts of "God Save the Queen".
Beside her, smartly attired in tails was Prince Philip who looked totally recovered from his recent illness and was in good spirits.
Following behind her were Prince Charles, the Duchess of Cornwall, who was chic in what is becoming for her a winning combination – an Anna Valentine dress and coat with a Philip Treacy hat.
In a third carriage, was Princess Eugenie who was the epitome of retro style in a teal number with black lace shoulder detail and a fishtail skirt, which was a remake of a vintage dress made for her by Christine Atkinson.
As with every event in the royal calendar this year, Ascot has been made even more special because of the Diamond Jubilee.
The racecourse was decorated with four kilometres of bunting, while many guests wore the red, white or blue of Union Jack as a nod to the occasion.
An exhibition is also being staged to coincide with the fixture, titled '60 Years of Royal Ascot during the Reign of Her Majesty the Queen'.
Johnny Weatherby, the Queen's representative at Ascot, said: "Royal Ascot has a long standing and privileged affiliation with the Queen, whose first winner at the event was in 1953 with Choir Boy who landed the Royal Hunt Cup."
And the famous horse owner's thoroughbred Carlton House was due to run in the Prince of Wales stakes on Wednesday.
Meanwhile, the final race, which is held on Saturday have been renamed in honour of her illustrious 60-year reign. Runners will compete at the Diamond – instead of the Golden – Jubilee stakes.
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