Also in attendance today from the royal family was Zara, 38, her husband Mike Tindall, 40, and Sophie Wessex, 54.
Camilla, wearing a pastel pink, shared her carriage with her husband and Prince William, who both wore a suit and top hat.
The royals warmly greeted each other and chatted as the 16 jockey and their horses were paraded around the royal enclosure.
Her Majesty was a social butterfly this afternoon as she went around chatting to family members.
Princess Eugenie, 29, Kate and Zara appeared to have an overdue catch up as they were seen grinning and embracing each other - all wearing various shades of blue.
Mike was seen joking with Prince William, 36, Sophie and even her Majesty at one point.
Prince Charles, 70, chatted with a mounted jockey, as he wore a grey top hat with grey suit, and blue shirt and pink tie.
Prince Edward and Prince Andrew kept a low profile during the family gathering.
Prince Will and Kate will be presenting the winning trophies in the King's Stand Stakes - a group one race - while acclaimed actor Sir Derek Jacobi will hand out the prizes for the Wolferton Stakes.
Writing in the opening day's official race programme, the Queen said: "Racing began at Ascot over 300 years ago and while much has changed, the horses remain the stars, thrilling us with their beauty, brilliance and courage.
"The quality and depth of competition at the royal meeting has also continued to prosper, with eight group one races taking place this week.
"The best horses and jockeys from across the globe are increasingly drawn to Royal Ascot, and it is truly exciting to welcome competitors from overseas, as strong international competition adds further interest and fascination."
Punters typically bet on the colour the Queen's hat, as bookies from William Hill falsely backed the colour pink - her Majesty arrived wearing pale blue.
William Hill spokesman Rupert Adams said: "The Queen's hat is one of the public's favourite fun bets and with the rain expected to hold off, the money says she will be pretty in pink."
Both Ladbrokes and Coral had cut the odds on the monarch wearing blue to even-money from 3/1 following a rush of wagers.
Alex Apati of Ladbrokes said: "We've taken a flurry of bets on the Queen wearing blue over the last 24 hours, forcing us to slash odds as a result."
Coral's John Hill said: "The colour of the Queen's hat is always one of the most popular betting markets at Royal Ascot each year, and we have already seen the first big gamble of the week as punters have been rushing in to back blue on day one of the meeting."
HEIR WE GO: The Queen's horses racing at Royal Ascot 2019
THE QUEEN is a keen racegoer and will attend Royal Ascot every day of the royal meeting (Tuesday - Saturday). She often seems at her happiest while at the races, and will no doubt be keeping an eye on her own horses as they try and romp to victory.
Her horses going for gold this year include:
Elector, trained by Sir Michael Stoute (running Wednesday)
Seniority, trained by William Haggas (Wednesday)
Eightsome Reel, trained by Michael Bell (Thursday)
Magnetic Charm, trained by William Haggas (Friday)
Sextant, trained by Sir Michael Stoute (Friday)
The Queen has attended every day of the meeting for the past 64 years and the last time she missed a moment of the event being her own coronation in 1953.
Her Majesty and the rest of the Royal Procession arrived at 2pm sharp before racing each day, half an hour prior to the first race.
The carriages leave Windsor Castle earlier in the afternoon and enter the racecourse through the golden gates before they pass the thousands of well-wishers in front of the grandstand.
The procession is a timeless tradition unique to Royal Ascot which dates all the way back to 1825.
The royal family weren't the only one to stand out today.
Commuters into London Waterloo station were among passengers affected, as well as race goers heading to Royal Ascot. Buses replaced trains on some routes.
This year's event is expected to attract around 300,000 racegoers over the next five days - which is predicted to be the wettest Royal Ascot over the next couple of days.
Leading bookmaker Coral has cut the odds into 6-4 (from 4-1) on this year’s Royal Ascot being the wettest on record as torrential rain is set to fall on the Berkshire Racecourse over the next couple of days.
We pay for your stories! Do you have a story for The Sun Online news team? Email us at [email protected] or call 0207 782 4368. You can WhatsApp us on 07810 791 502. We pay for videos too. Click here to upload yours.