(CNN) -- They think it's all over... it is now.
Britain's Queen Elizabeth II's filly Estimate came tantalizing close to defending her Gold Cup title at Ascot only to be edged out by a neck by a fast-finishing Leading Light in one of the most thrilling finishes in Gold Cup history.
A superb ride by Joseph O'Brien on Leading Light ensured that Estimate's jockey, Ryan Moore, did not have things all his own way as they rounded the final bend.
The two-and-half mile race came down to a sprint finish between Leading Light, Estimate, and Irish raider Missunited, who clung on to finish third, having made all the running.
Also bidding to spoil to the royal party was Brown Panther, owned by former England footballer Michael Owen. He held on gamely to finish fourth.
It's not often you see two national treasures go head-to-head at Royal Ascot, but Owen himself is popular figure in the paddock these days, having enjoyed a successful second career as an owner and breeder.
Day three of Ascot is also Ladies' Day, which is always guaranteed to provide a glittering array of frocks and hats.
The Queen herself, who was wearing blue, was gracious in defeat, presenting the trophy to the winning owners.
"It was tremendous and the Queen got such pleasure out of it.," said John Warren, her racing manager, of Estimate's performance.
"To see her put in such a brave effort like that was tremendous. It was a career best. She ran as good as you could ever hope."
Estimate's trainer Sir Michael Stoute added: "It was a great run and I'm very proud of her."
Missunited's trainer Michael Winters was also pleased with his runner: "She's run her heart out and jockey Jim Crowley has given her a peach of a ride," he told reporters.
"There was a moment down the back straight when I thought she might have given them the slip but it was a super run and a great ride."
Leading Light's victory made it a double on the day for the O'Brien camp, as the trainer and his son had earlier opened their account with Bracelet in the Ribblesdale Stakes.
Unusually, the 10/1 shot was the pair's first winner of the week.
"We're delighted to get a winner," conceded her trainer. "She's traveled and quickened well off a nice even pace," added her jockey.
Earlier in the day, Baitha Alga struck in the Norfolk Stakes to give Frankie Dettori his 49th winner at the Royal Meeting.
"I'm nearly there," exclaimed Dettori of his looming half century.
"It was a great performance. He's hard as nails and uncomplicated - everything you want in a two-year-old.
"I just had to do the right thing, get into the race and use his turn of foot," added Dettori, who celebrated the win with his trademark flying dismount.
There was another milestone for Stoute as victory for Cannock Chase in the Tercentenary Stakes gave the trainer his 70th Royal Ascot victory, making him the most successful living trainer at the meeting.