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Racegoers are preparing for Gold Cup Day, also known as Ladies' Day, one of the highlights at Royal Ascot.
Ladies' Day is known for its display of flamboyant and exotic hats and the most extravagant creations.
Racegoers also traditionally bet on the colour of the hat the Queen will wear on the day.
Bookmakers Coral believe she will wear a blue hat and makes the colour its 3-1 favourite.
However, punters have been backing purple and its odds have fallen from 8-1 to 5-1.
The Queen will be hoping her horse Estimate triumphs in Royal Ascot's Gold Cup today as the famous race stages its Ladies' Day.
Over the years the Queen has had 21 winners at the Royal Ascot. This year her filly is a favourite to win.
Gary Lineker, Katherine Jenkins and Aishwarya Rai Bachchan were among the famous faces who visited Royal Ascot today.
The famous five day meeting at the Berkshire racecourse is known for its array of celebrity visitors as well as its racing.
Welsh classical singer Katherine Jenkins said she was attracted to the glamour of the event: "I love Royal Ascot, it's just so old-fashioned - old-fashioned glamour, old-fashioned traditions."
The monarch, who is a passionate horse owner, was greeted with cheers as she rode into the famous racecourse in a carriage with the Prince of Wales and the Duchess of Cornwall.
Ascot hosts the famous five-day meeting which is as much a social event as an important sporting fixture that attracts some of the best thoroughbreds, jockeys and trainers in the world.
The Queen wrote in the official programme: "I was fortunate enough to own a winner at last year's royal meeting, so I know what a thrill it is to have success at this wonderful racecourse, whether you are a trainer, jockey, or one of the many hard-working stable staff associated with every runner.
"I would like to wish all those involved the very best of luck."
- 10:30 Gates Open
- 14:00 Royal Procession
- 14:30: The Queen Anne Stakes
- 15:05: The King’s Stand Stakes
- 15:45: St James's Palace Stakes
- 16:25: Coventry Stakes
- 17:00: Ascot Stakes
- 17:35: Windsor Castle Stakes
- 18:00 Singing around the Bandstand
Bookmakers are taking bets on the colour of the Queen's hat for Ladies' Day on Thursday with pink the favourite at 4/1.
But, blue at 6-1 has been by far the most popular choice, with whichever colours the Queen choose for today and Wednesday also likely to influence the betting before the big day.
Thousands of racing fans will today pay their respects for first day of Royal Ascot to legendary trainer Sir Henry Cecil, who died last week at the age of 70.
The Newmarket trainer was a 10-time champion racehorse trainer and one of British racing’s most famous personalities as well as one of the industry's most respected trainers.
He won 25 British Classics, including the Derby on four occasions and had no fewer than 73 Royal Ascot victories to his name.
Following the traditional pre-racing procession down the course, which will be headed by the Queen, a minute’s silence will be held in honour of Cecil.
The Queen will attend one of the highlights of the racing calendar today, the Royal Ascot, without the Duke of Edinburgh - who is recovering after exploratory abdominal surgery.
The world-famous annual meet is as much a social event as an important sporting fixture and it attracts some of the best thoroughbreds, jockeys and trainers in the world.
The Queen's horse Estimate will run in the Gold Cup on Thursday and is a favourite with some bookmakers.
She will start off the festivities today by taking part in the traditional carriage procession along the course.