Ridden by Olivier Peslier, the 4-1 second favourite, on his debut in Group One company, raced clear at the 400 metre mark and came right away from Irish Derby winner Cape Blanco (9-2).
Harbinger beat the course record time by just under half a second in an electrifying display which prompted one bookmaker to slash the four-year-old from 8-1 to even money favourite for the Prix de L’Arc de Triomphe in October.
It was a fifth success in the King George for trainer Michael Stoute who first enjoyed a winner in the big race back in 1981 with the ill-fated Shergar.
Harbinger, a still improving horse, is owned by the Highclere Thoroughbred Racing syndicate who enjoyed success in the Epsom Derby with Motivator in 2005.
Stoute told BBC TV: “Olivier was just cantering. He travelled so well and he was looking good from a long way out.”
Workforce, who won last month’s Epsom Derby in record breaking-time, started a warm 8-11 favourite but struggled to go Saturday’s pace as the six-strong field moved into the straight.
Stable jockey Ryan Moore, who opted to ride Workforce instead of Harbinger, blamed the firm ground for his colt’s defeat.
UAE leads both the Ladies’ Team and Under-15 Girl’s Team divisions at Riyadh Golf Club tournament