Charles and Camilla arrived by car and not the traditional carriage procession, and were watched by some of the public waiting for the racing to begin.
Punters were hoping the Queen would make an appearance but a few caught a glimpse of a group of royal women arriving at the Berkshire meet.
The Princess Royal was joined by her daughter and son-in-law Zara and Mike Tindall and the Countess of Wessex was also seen arriving at the racecourse.
The Queen did not join racing fans at the start of the five-day meet, choosing instead to watch it on television at Windsor Castle
She has a runner, King’s Lynn, in the 15.40 King’s Stand Stakes.
The Queen’s racing manager John Warren has said the monarch, a keen horse breeder, is hoping to attend the Berkshire racecourse later in the week.
Mr Warren described how horse racing offers the monarch a “very broad escapism” from all that she has to deal with in her life.
He described the head of state as “fanatic” about horse racing, and said her energy levels were “incredible” despite being five years away from turning 100.
Mr Warren told BBC Radio 4’s Today Programme on Tuesday: “It’s remarkable. The Queen’s energy levels are incredible. She’s 95.
“She went down to the G7 this week, and trundled back on the train in the middle of the night and the energy will be raised higher again for a week like Ascot.”
The Queen has a number of runners at the Berkshire racecourse, with Mr Warren tipping Tactical in the Jersey Stakes on Saturday as a potential winner.
Racegoers are being welcomed back to Royal Ascot for the first time since the pandemic began.
Punters dressed in outlandish hats, summer dresses and smart suits will cheer on the jockeys over the next five days.
Mr Warren added: “Obviously the Queen would love to attend, as you know she’s fanatic about racing, watching racing and breeding horses, and has been going to Ascot all of her adult life.
“So, it’s a shame to miss an event.
“The plan at the moment is to see how it goes towards the latter part of the week and if the Queen’s able to come because she’s got runners, then, fingers crossed, it will happen.”
There will be no traditional carriage procession if the Queen does makes an appearance.
The monarch will also not be able to examine horses in the paddock, as she usually does, because of the Covid restrictions on movement between areas.
Mr Warren said: “In the past, she would have gone and looked at horses in the paddock, even though they weren’t hers because she is so fascinated in the breed so she’d want go and look at the stallion prospects of the future.”
He described how the Queen scrutinises the winners of every race daily to see if the stallions offer potential for breeding.
“Every race that takes place every day of the week, the Queen will certainly read the Racing Post every morning, look at the breeding of all the winners the day before, and see that these stallions that she uses will be potential horses for her own mares,” he said.
“It’s a deep fascination, a very broad escapism for all the other things that the Queen has to deal with in her life.”
The monarch, who is the nation’s longest reigning sovereign, has kept busy with her duties as head of state since the death of the Duke of Edinburgh in April.
The royal family has also experienced a turbulent time with the Duke and Duchess of Sussex’s Oprah interview and Harry’s criticism of his family on other programmes and podcasts.
Bookmaker William Hill has already opened a book on a favourite bet among racegoers, the colour of the Queen’s hat, with blue the early favourite with odds of 3-1.
Ascot was staged behind closed doors last year but this year was selected to take part in the Government’s Events Research Programme on behalf of the sport of racing.
Each day 12,000 racegoers will be allowed to watch the sporting spectacle after providing negative Covid-19 tests.