Dettori punched the air as he recorded his 79th victory at the meeting on Courage Mon Ami where he had his first on Markofdistinction in 1990.
The 52-year-old described the win as "unbelievable" before the irrepressible Italian broke protocol by kissing Queen Camilla - he had also kissed his manager Peter Burrell on the lips on the way back to the winner's enclosure - as she and Charles presented the trophies.
Dettori, who is enjoying a successful final year in the saddle having won the English 2000 Guineas and Oaks, then threw the trophy up in the air and fortunately caught it.
Winning trainer John Gosden, who shares the duties with son Thady, praised Dettori for a "great ride".
Gosden was beaming, in contrast to his gloomy expression after Dettori gave the great stayer Stradivarius a much-criticised ride in last year's Gold Cup - as a result, trainer and jockey split for a short time.
"That crowns Frankie's week now," said Gosden.
"It has been 30 years working on and off and we have had one argument in all those years.
"How many marriages can you say that of? We had a disagreement and kicked on, that is life."
Charles and Camilla had been on the receiving end of the presentation after Desert Hero won the King George V Stakes - Charles's first Royal Ascot as monarch since succeeding his mother, the late Queen Elizabeth II.
Both Charles and Camilla wiped away tears in the Royal Box as Tom Marquand got their horse past Valiant King to take the honours.
They descended from the box to the winner's enclosure, the king with a broad smile on his face as he shook hands with Marquand and trainer William Haggas.
The royal couple then accepted the trophy from the Duke of Kent with Princess Anne and her daughter Zara Tindall looking on.
"I am thinking of how proud the Queen would have been for Charles and Camilla to have a winner and keep the dream alive," said Zara.
"It is a new excitement for them. Like all those owners who have a horse here, they are living that dream and hope and fulfilling it is incredible."
'Great for the small man'
Valiant King may not have prevailed but Valiant Force did in the opener, the Norfolk Stakes, at the extraordinary price of 150/1 - a second win of the meeting for jockey Rossa Ryan.
"Be fair to the lads, they were confident he would run a big race," said Ryan.
"I was just in a rhythm and probably could have won more. Job done."
One bookmaking operation paid out at odds of 487/1 for the winner trained in Ireland by Adrian Murray.
Murray is developing a habit of producing big-priced winners having welcomed home 125/1 shot Kodi Bear in the more prosaic setting of Fairyhouse last July.
"It's brilliant, I just cannot believe it. I fell into racing by accident," he said.
"It's the stuff of dreams. It's great for the small man."
Dettori will hope to finish the week ahead of his rivals still riding in terms of overall Royal Ascot winners - Haggas' late father-in-law Lester Piggott's extraordinary total of 116 remains the benchmark.
However, Dettori is being pressed hard by Ryan Moore, whose win in the Ribblesdale Stakes on Aidan O'Brien's Warm Heart took him on to 77. For O'Brien, it was a record-extending 84th victory.
"He's an incredible fellah," O'Brien said of Moore.
"He is nearly 40 but he gets better every year.
"When he comes to Ireland to stay with us he runs 6-10 miles every morning before he rides the horses.
"He is cool under pressure and a total professional."
