Estimate raised the roof at Royal Ascot by providing the Queen with victory in the Gold Cup.
Trained by Sir Michael Stoute and ridden by Ryan Moore, the four-year-old filly become the first horse owned by a reigning monarch to win the two-and-a-half-mile showpiece.
The 7-2 favourite was challenged strongly inside the final furlong by Simenon and French raider Top Trip, but Estimate stuck her neck out gamely for a famous success.
Estimate won at the meeting last year in the Queen's Vase, returning to action this season with victory in the Sagaro Stakes, after which she was promoted towards the head of the Gold Cup market.
Despite the bookmakers fancying her chances, Stoute had always urged caution, suggesting her form did not entitle her to be favourite and that her position in the betting owed more to who owned her rather than her actual chance.
In the perfect position throughout, Moore tracked last year's winner Colour Vision into the straight before striking for home.
Simenon, twice a winner at last year's fixture, looked to be coming with a race-winning run under Johnny Murtagh for Willie Mullins but could never quite draw level with Estimate, while Top Trip tried to force his way between them.
Showing incredible guts and determination, Estimate won by a neck.
Estimate is bred to win the race being a half-sister to 1999 winner Enzeli.
Moore said: "We've always had this race in mind, she won well.
"It's fantastic to ride a winner here for the Queen and in the Gold Cup, it's very special.
"She was holding them."
Stoute said: "She had to show a lot of courage as she had to beat one and then stave off another.
"He (Moore) always had her in a good position and she switches off so well.
"I really felt it was a seriously tough task for her, I couldn't be confident at all taking on the boys that are proven over this trip and she can be a pain in the backside at times."
Asked what it meant to train a Gold Cup winner for the Queen, the trainer said: "It's a great honour and a tremendous thrill. We know how much she loves this game."
Stoute, who was winning the Gold Cup for the second time in its 207-year history, went on: "It's a huge thrill as I wasn't confident.
"Her preparation had gone well and she was bred to have a big chance of getting the trip but she had to step up from the Sagaro to beat these boys. I was realistic - I try to be that.
"She had to work hard to get the grey horse of Godolphin and then she had a second battle with Willie Mullins' horse. Watching, it was tense and very long.
"She's so full of guts and so courageous, and she's very relaxed in her races. I think she'll have a good rest now, as that was a very hard race.
"It's a special thrill for the Queen.
"She said it gave her great pleasure and she thanked everyone involved.
"Racing is a big recreation for her, and with her breeding programme, it will have been a bigger thrill than if it were a colt."
Mullins, better known for his exploits in the National Hunt sphere, said: "He's run a career-best, which I said he might have to, and we're very pleased.
"We're a little bit disappointed as at the furlong marker I thought maybe (he could win), as Johnny (Murtagh) is in such form, but of course Ryan Moore (won it) on the Queen's filly and she had the greater form.
"It's probably a fantastic result for racing. I would have loved to have won and I'll probably never be in this position again - hopfully one day.
"The stands just erupted from about the furlong marker and everyone was rushing from the front of the stand as everyone wanted to get a position here (around the winner's enclosure).
"It's a fantastic day and there's a fantastic atmosphere here now.
"We want to take our horse to the Melbourne Cup. I'll start making plans when I get home. It's going to make November a little busy."
Top Trip's trainer, Francois Doumen, said: "I would have preferred a diplomatic incident and won the race!
"The winner is magic. Our horse has run well the first time at this distance and he looks like a promising Kasbah Bliss.
"He'll go for the Prix du Cadran at Longchamp in late September. We had the horse entered in the Arc, but it's too delicate a situation to talk about that at the moment.
"We bred the horse with the owners."
Simon Crisford, racing manager for Godolphin, said of Colour Vision, who was fourth this time: "We couldn't be more pleased with him.
"He's run a magnificent race and he will follow the same programme as last year."
Video: Queen's horse wins Gold Cup