Conduit led home stablemates Tartan Bearer and Ask as Sir Michael Stoute executed one his greatest training feats in the King George VI and Queen Elizabeth Stakes at Ascot.
Aidan O'Brien's squad occupied the leading positions for most of the way but once in the straight the Stoute trio surged past and had the race between themselves.
Ryan Moore drove Conduit (13-8 favourite) into the lead in the final furlong and beat Tartan Bearer, in the same Ballymacoll Stud colours, by a length and three-quarters, with Ask a further head away in third spot.
There was a stewards' inquiry as Conduit appeared to cross Tartan Bearer slightly in the closing stages, but the placings remained unaltered, although Moore picked up a three-day ban for careless riding.
Stoute, securing a fourth King George after Shergar (1981), Opera House (1993) and Golan (2002), said: "I've always loved this race and this hasn't quite sunk in yet. I'm very proud of them - they've all run great races.
"It ranks very high among my career achievements - this is a bit special. We were hoping one of them would win and it's a great thrill to see them perform to such a high standard."
Moore added: "There was a good pace and it set up nicely for him. When he got to the front he just had a little look and shifted right, as he has done in the past.
"He won the Breeders' Cup last year and from then we knew he was going to be a King George horse, but we didn't think we would have the three horses in it."
Conduit and Tartan Bearer are both owned by Ballymacoll Stud, and racing manager Peter Reynolds noted: "That is our 50th Group One win, and Michael's 10th individual and 20th overall Group One for Ballymacoll - which isn't bad!
"It's great to keep the firm up there. We are competing against some heavy hitters in Sheikh Mohammed and John Magnier's team and it is nice to have something to take them on with."