They've been saying it since they first set eyes on the scrawny kid from Co Down with crazy hair and an oversized putter in his hands.
‘They' are the people who know their sport. People like Darren Clarke, who took one look at the 10-year-old Rory McIlroy and thought: “My God, this boy's a genius.” And they were right. The golf world has known for a long time how special Rory is. And now we all know.
There have been hints, of course. He has led major championships before, but even journeyman have done that.
He has won minor tournaments, but who hasn't? He's even been part of a successful Ryder Cup team, but only the most churlish ‘Wee-Mac' fan would deflect any of the glory for that away from his compatriot Graeme McDowell.
Of course, there was the ‘Masters meltdown' two months ago.
The kinder critics that dreadful day in Augusta described it as McIlroy once again exemplifying a penchant for “unfulfilled potential”. The less generous ones used the ‘c' word — a word so nauseating to the 22-year-old that he couldn't even repeat it.
They can use that word as much as they want now. Rory was certainly a ‘choker' at the Congressional Club.
He choked the life, the spirit, the competitiveness out of the best golfers on the planet, made them look ordinary, left them — and the lingering doubters — floundering in a fog of bewilderment, shock and awe.
This wasn't just golf. This was a devastating display of sheer, jaw-dropping, God-given talent. It was spine-tingling to see an artist deliver his masterpiece in such a breathtakingly, seemingly effortless, way.
The Holywood star's rivals now know how the bitter composer Salieri felt when he sneaked a look at Mozart's sheet music, let the master's ethereal notes drift through his head — and ended up in an asylum.
Even Rory's great friend McDowell — who won this very tournament only a year ago — said: “When you see Rory playing like that, you start to wonder if you can play golf at all.”
We woke up to McDowell's stunning victory at Pebble Beach because most of us had gone to bed believing he'd only a fighting chance of achieving it.
We were wide awake all throughout this one. And, yes, of course we were thinking about what happened at the Masters. And hoping Rory wasn't.
We needn't have fretted. Rory led for three and a half rounds in Augusta but still never looked at ease with himself.
This time, it was different. This time, there was an inevitability about where it would end — on the 18th green, with tens of millions watching, and with a delirious, delighted (and, yes, probably relieved) young man, a newly-crowned US Open champion, embracing proud parent Gerry on Father's Day.
We're used to our sports stars punching above their weight. The word ‘underdog' could have been invented for us.
Nobody expected Mary to win gold at the Olympics, nor Gerry to score that goal against Spain. Surely Barry couldn't get the better of Pedroza, nor Dennis the invincible Steve Davis?
G-Mac? Well, no European had won the US Open since 1970 — and no Ulsterman had bagged a major since Fred Daly, clinched The Open in 1947...
This feels different, though. McIlroy's brilliance over the past few days will surprise no-one, not even the sneerers who labelled him ‘the lost boy of Augusta' two months ago.
Forget his current ranking of seventh; on the evidence of this triumph, Rory is the best golfer in the world, with the potential to be the best of all time. Yes, he's that good.
And, yes, this wee country has produced sports people who can feel entitled to lay claim on such lofty credentials.
Alex Higgins is one — and, if you close your eyes when listening to Rory talking, you may well think of another.
That lovely, lilting Ulster accent, the inflections and tones that project modesty, yet also enunciate an unshakable belief in the speaker's own, awesome ability... yes, you could be listening to Bestie. You're certainly listening to a genius.