Roberts, the champion jockey, and Sheikh Mohammed, Opera House's owner and the globe's foremost payer of horse-bills, appeared to be racing's dream ticket when they teamed up at the beginning of this season, but it took until yesterday for the results to match the billing.
Roberts's chagrin has been exacerbated by a series of suspensions this term but, when he starts a 10-day ban after riding in Istanbul today, he will be warmed by memories as well as the weather. 'We (jockey and owner) have won other Group Ones together but the King George is something else,' he said.
Opera House's victory here, the first by a five-year-old since another Roberts-ridden horse, Mtoto, in 1988, was achieved in drizzle and also plopped a series of statistics into the waste-paper basket.
For much of its recent history, the King George has been barely more than a victory parade for the season's leading three-year-old and there has been a creeping belief that the conditions of the race prohibit success for an older horse.
Here, though, was evidence that ability as much as anno domini was an influence on a particularly well-contested race. This was a congregation of the turf's earnings heavyweights, with Desert Team the only entrant to fall below pounds 160,000 in career earnings.
Opera House, who would probably never have been here had a pastern injury not stalled both his career and a life at stud, has improved with age, but there has always been a suggestion that the final spark of brilliance was missing from his armoury.
Michael Stoute, the horse's trainer, has tired of the adjectives 'honest', 'dependable' and 'consistent' being appended to his charge. 'Now you will have to say he is good as well,' the Newmarket man said.
Opera House is considered to be an animal who operates on all types of going, but if he does have a preference it is for the spongy turf that was laid before him yesterday. 'We always prefer a bit of juice in the ground for him and so we were pleased with the condition of the track,' Stoute said. 'We train the horse in a certain way and we knew he was well.'
Mere well-being, however, is not enough to win a King George. Stoute knew his horse would have more behind him than in front, but could not envisage victory with any great clarity. 'I wasn't entitled to be over-optimistic in a race like that,' he said, 'but I knew he wouldn't be out of the frame.'
The first out of the stalls was the filly User Friendly, who towed the field round for much of the race, her head raised in its usual clumsy manner as if peeping over a garden fence.
Clive Brittain, her trainer, was later to report that User Friendly was never allowed the comfort of a breather at the head of the pack, which contributed to her back- pedalling at the entrance to the straight.
By that time, Roberts had been rehearsing his winners' enclosure chit-chat with the Queen. 'We were stuck out a bit wide, I was out four deep which I didn't want to be, but we were travelling smoothly,' the South African said. 'Looking around at the six (furlong pole) I didn't think I would get beaten.'
Opera House, though, had still to overtake Commander In Chief, who struck for home as User Friendly petered out. For once, though, the yawning stride of Henry Cecil's colt failed to take him clear of his pursuers and Roberts crept by stealthily.
Commander In Chief soldiered on, but the exertion of five previous races this season allowed Peter Chapple-Hyam's White Muzzle to run him out of second place. Cecil could have found sanctuary in his runner's active season as an excuse but refused. 'He was beaten by a better horse on the day,' he said.
His views were endorsed by Chapple-Hyam. 'Take nothing away from Opera House, he beat us fair and square. But for me White Muzzle is still a winner,' Chapple-Hyam said.
Christy Roche got a two-day ban (3-4 August) for use of the whip on Desert Team (seventh).
Having proved the high-summer champion of Britain, Opera House will now attempt to extend his hegemony to Europe in the autumn. A bunch of King George winners have appeared debilitated characters in racing's late season and Stoute is already pondering how to preserve his horse's powers for the Prix de l'Arc de Triomphe.
'He will definitely be trained for the Arc but I'll have to think long and hard about which route we'll go,' the trainer said.
Ladbrokes' reaction was to install Opera House as the 5-1 favourite for Longchamp, and spectators will have just one more racecourse opportunity to assess if that is a kind price.
A single spectator caused consternation yesterday during the King George presentation ceremony. After shaking hands with Sheikh Mohammed, Roberts and Stoute, the Queen may have been mildly surprised to find an interloper, later described as a Brighton undertaker, taking his turn to press the Royal flesh.
The monarch escaped with nothing more than a start, but this breach of Ascot's renowned security procedures must have meant that Roberts and King George analysts were not the only relieved parties last night.