Adayar became the first Derby winner to follow up with a victory in the King George VI and Queen Elizabeth Stakes for 20 years, at Ascot.
The Charlie Appleby-trained colt finished a length and three-quarters clear of runner-up Mishriff, with Love in third.
Galileo was the last horse to complete the Derby-King George double in 2001.
"I am a bit speechless. He just gives you the feeling of endless power," said jockey William Buick.
The race had been dubbed a battle of the generations and racing's superpowers, with Adayar representing Sheikh Mohammed's Godolphin team, and dual Classic winner Love trained by Aidan O'Brien for the Coolmore team.
However, Adayar always looked to be travelling well and when Buick gave the signal at the top of the straight, he lengthened his stride to assume control.
Mishriff, who raced at the back of the five-runner field, made significant headway in the final couple of furlongs.
But Adayar was already well clear and galloped to the line to give Appleby a first King George win.
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