The three-year-old supplemented his wins in the Queen's Vase at Royal Ascot and the 12-furlong Grand Prix de Paris at ParisLongchamp when adding a Classic verdict to his CV on Town Moor.
While he saw out the mile and six furlongs at Doncaster in fine style, O'Brien revealed winning jockey Ryan Moore thinks he may have more to give over lesser trips.
He said: "I said that (he could be a Cup horse) to Ryan and he kind of thought that maybe he wouldn't have to do that, that he wouldn't have to go Cup trips. He'd have no problem doing it, but Ryan didn't think he'd have to."
Given Kew Gardens has already scored over the course and distance of the Prix de l'Arc de Triomphe, O'Brien was not ruling out a crack at the autumn showpiece next month.
He added: "He could be (an Arc horse), he could be anything like that.
"We were delighted. We were very happy throughout the race and I think everything went fair enough. He's a solid horse and always has been. A very solid, uncomplicated horse."
Sky Bet make Kew Gardens a 20/1 chance for the Arc, in a market topped by last year's winner Enable at 11/8.
O'Brien and Moore faced a mad dash to Leopardstown following their Classic victory, with Saxon Warrior finishing a narrow second for the pair in the Qipco Irish Champion Stakes.
The trainer admitted there had not been much time to reflect on Kew Gardens' win immediately after the race.
He added: "I was watching it on the big screen and there was a lot happening, we had to get out of there very quickly!
"We didn't get a chance to look at any replays.
"We got a helicopter from Doncaster to Doncaster airport, then a plane from Doncaster airport to Dublin and a helicopter from Dublin to Leopardstown.
"We're delighted that everyone gave us a chance to get there and we appreciate it."
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