Trainer John Gosden has won his first Ascot Gold Cup and jockey Frankie Dettori his sixth with Stradivarius prevailing over Vazirabad.
Stradivarius was the equal favourite with the Lloyd Williams-owned Order Of St George who ran fourth.
Gosden said the Melbourne Cup was a race connections would consider.
"It is lovely to win it. I've been placed in it, but you have got to have the right horse. He is a dear horse and he is not very big," Gosden said.
"I didn't put him in the King George as win, lose or draw, we were going to go back to the Goodwood Cup, but he is in the Arc.
"The Melbourne Cup is a very attractive idea as well. We've got to get to Goodwood, but let's enjoy today."
Dettori, who missed the ride on last year's winner Big Orange through injury, racked up his 60th Royal Ascot winner on Stradivarius.
"Ryan (Moore, on Order Of St George) was in trouble four out, but I thought it could be deceiving because if I attacked him then, he might battle me out of it," he said.
"As I got rid of him, I could see this grey head (Vazirabad). He managed to get within a neck and once he couldn't get past me, I knew my horse was brave and that was it.
"The crowd got behind it. It was mental and I was loving it. To get the three best horses battling it out, you can't get much better than that. Full credit to the horse - he was brave as a lion."
American trainer Wesley Ward had his spirits lifted after the failure of Lady Aurelia when Shang Shang Shang held on by a nose to take Group Two honours in the Norfolk Stakes.
"To win this race with a filly is just unbelievable," he said.
"I come here every year and we were scratching our heads the first two days and we were going back to the beginning wondering if we were in the right place.
"It's a win-and-you're-in (race), so ultimately we want to go to the Breeders' Cup. We'll work back from that."