Charles and Camilla were a picture of delight as their thoroughbred Desert Hero, an 18-1 longshot, crossed the line first in a photo-finish.
The late Queen, who was a passionate racehorse owner and Royal Ascot stalwart, would have been “proud and excited” for the couple, said Zara Tindall, the King’s niece, who joined him in the royal box.
As they watched the final moments of the race, run over a mile and four furlongs, the Queen waved her official programme in the air in excitement and Charles looked across at his wife in joy at the end.
The couple clearly have the racing bug and their first win made up for two days of frustration, watching their previous Royal Ascot entrants beaten on the track this week.
When the victory was confirmed by the race track announcer the thousands packed into the stands cheered.
Mrs Tindall said afterwards: “It’s bitter sweet isn’t it, just think how proud and excited our grandmother would have been, the Queen would have been.
“To have a winner for Charles and Camilla and to keep that dream alive was incredible, and what a race – asides all of that, what a race.”
She added: “I think it is a new excitement (for the King), like all those owners who come here and have a horse here, having that dream, that hope and actually fulfilling it is incredible.
“And the horses are the main game here, that’s why we get involved and we love them and the competition, and the adrenaline when you win is indescribable.”
As the winning owners, the King and Queen came down from the royal box to the parade ring to receive their trophy and shook winning jockey Tom Marquand warmly by the hand, with Charles, grasping it as they spoke.
They were joined by John Warren, their racing and bloodstock adviser, who earlier this week said the couple were very much looking forward to a week of racing.
There was a little mishap when the King returned the trophy to the presentation table and it tipped over with a clang before he set it down safely.
Charles and Camilla’s first win opens their Royal Ascot account, but they have a long way to go to eclipse the late Queen who had more than 20 victories during her 70-year reign at the racecourse.
The King and Queen were soon back to present the winning trophies in the Gold Cup, the most popular race of the week, which saw jockey Frankie Dettori win on the horse Courage Mon Ami.
Dettori kissed the Queen on the cheek and he threw the trophy in the air and just caught it before quickly returning it to the table.