Doyen justified his status as hot favourite to win the King George VI and Queen Elizabeth Diamond Stakes at Ascot.
Frankie Dettori took the 11-10 shot to the front two furlongs out and from then on the result was never in doubt.
The four-year-old then cruised home to give Dettori, who had earlier ridden his 2,000th British winner, his fourth King George victory.
It was also a fifth win in the £750,000 contest, run over 1m 4f, for Godolphin trainer Saeed bin Suroor.
The American-trained Hard Buck held off Godolphin's fast-finishing second-string runner Sulamani for second.
Lunar Sovereign, Godolphin's other runner in the race, set a slow early pace but then quickened up at the six-furlong marker to open up a three-length lead.
However, by the time the field turned into the home straight, he had been pegged back by the chasing pack.
Doyen, who also won at Royal Ascot last month, then accelerated to leave the rest trailing in his wake and capture his first Group One success by three lengths.
Dettori, after performing his second flying dismount of the afternoon, described Doyen's performance as "absolutely devastating".
He told BBC Sport: "What a great horse he is. Now we can really say he is one of the finest. The King George is a special race and Doyen is a special horse."
Godolphin supremo Sheikh Mohammed, who also bred the colt, added: "The sky is the limit. He is ready for all the big races here, in America, and around the world."
The King George VI and Queen Elizabeth Diamond Stakes, one of the biggest races on the Flat calendar, also forms the third leg of the World Series, an international horse racing championship.
King George VI and Queen Elizabeth Diamond Stakes (Group One)
1 Doyen (L Dettori) 11-10f
2 Hard Buck (G Stevens) 33-1
3 Sulamani (K McEvoy) 7-1
11 ran. Dist: 3l, hd.