Roca Tumu was a 20-1 winner of the Britannia Stakes to give Ireland a seventh winner of the week at Royal Ascot.
The inexperienced colt was having just the fifth run of his career and provided trainer Joanna Morgan with a first winner at the meeting.
Billy Lee had his mount settled close to the pace set by Shebibi, unlike the well fancied duo of Wentworth and Cape Peron who both had too much ground to make up eventually.
In the end is was Godolphin's Tarikhi who made the winner pull out all the stops but went down by a neck.
Queensberry Rules was third with Wentworth closing into fourth.
"He's very straightforward and a great horse to ride. He has a beautiful nature. It's brilliant" - Billy Lee
Lee said: "I got there (the front) a bit sooner than I'd like, but he's a gutsy horse and in fairness, when the second horse came to him, he battled on again.
"He's very straightforward and a great horse to ride. He has a beautiful nature. It's brilliant.
"The owners will enjoy this."
Morgan said: "I could retire after this. I'm so delighted - it can only go down from here!
"We nearly didn't get here. Some of the owners wanted to sell him and more didn't. Thank God they didn't sell him.
"A month ago I thought we could (win), but the closer one gets to the race the more you get butterflies.
"He's a very able horse. It's absolutely great."