Aidan O'Brien's So You Think won the Prince of Wales's Stakes at Royal Ascot in the race's 150th anniversary.
The odds-on favourite saw off the challenge of the Queen's horse Carlton House to win by two and a quarter lengths.
It was a first victory at the meeting for trainer O'Brien's 19-year-old son Joseph, and a 10th Group One win for So You Think.
O'Brien snr said: "He's one of those special horses that can travel and has class. We were delighted with the ride he got, Joseph knew what he wanted to do."
Carlton House finished second with Farhh half a length back in third.
It means the Queen's wait for her first Group One victory in Britain since Dunfermline's triumph in the St Leger in 1977, continues.
She has two more chances for success this week - Momentary in the Ribblesdale Stakes on Thursday, and Estimate in Friday's Queen's Vase.