“Harbinger is pulling right away from the Derby winner, and the Irish Derby winner – he’s going to win by a street” was the call from the BBC’s Jim McGrath on what was arguably the greatest performance ever seen in the King George VI And Queen Elizabeth Stakes.

Sadly a career-ending injury meant we never got to know if he really was as good as he looked on that day in 2010, but the form book certainly went on to back him up.

The Derby winner in question was his Sir Michael Stoute-trained stablemate Workforce, who eventually finished fourth but bounced back to win the Prix de l’Arc de Triomphe.

Cape Blanco, the Irish Derby winner, went on to win the Irish Champion Stakes by the small matter of five and a half lengths and added three more Grade Ones in America the following year.

Youmzain was third, having already finished second in three runnings of the Arc, while Hong Kong Vase winner Daryakana was fourth, so it is almost impossible to pick holes in the form.

That is before you even look at a stopwatch. Harbinger smashed the previous course record, taking almost half a second off it. Perhaps those who often claim something is too good to be true might just have to eat their words on this one.

Of course, the crying shame is that he suffered an injury on the gallops just a couple of weeks later when being prepared for the Juddmonte International and while he managed to have a successful second career at stud in Japan, he never raced again.

Harry Herbert, managing director of Highclere Thoroughbred Racing who owned Harbinger for his racing days, takes up the story.

“You have to pinch yourself because it was such an extraordinary performance. Olivier Peslier had ridden him in his last piece of work and said ‘he’ll win the King George and he’ll win the Arc’,” said Herbert.

“When he won that day it was the most remarkable performance of any horse we’ve had anything to do with. Sir Michael admitted in a video we put together after it that on the day he was the equal or better of Shergar.

“I think what was most extraordinary was that not only did he beat two Derby winners by 11 lengths and more, he absolutely smashed the track record.

“It was just a tragedy that he never ran again because Workforce, behind him that day, went and won the Arc.”

“There is a wonderful reverse camera angle of the race where you see Olivier ask the horse for his effort and he surges forward and pushes Olivier back in the saddle. He had such extraordinary power.

“It really was one of the all-time great performances, one that you can’t quite believe what you are seeing. It earned him the accolade of World Champion Racehorse for that year.”

Unraced at two, Harbinger had promised to be a good horse at three, winning a traditionally strong Chester maiden, skipping the Derby but then winning the Gordon Stakes, before failing to show his true colours in the Great Voltigeur and St Simon Stakes.

“We hadn’t completely ruled the Derby out when he won his maiden at the Chester May meeting, but Sir Michael just felt he needed more time and we were happy to go along with that,” said Herbert.

“He won the Gordon Stakes at Goodwood, but then flopped in the Great Voltigeur and was then beaten in the St Simon at Newbury.

“We found after that he was just displacing his palate. He had some tiny laser surgery to correct that and then he became the machine we saw at four.”

Herbert went on: “He was an extraordinary racehorse and it was a tragedy he never ran again as the plan was to go to York and on to the Arc.

“We contemplated whether he could race again after his surgery, but that would have been odds against and there was a very big bid from Japan for him to go to stud out there and he’s been a very successful stallion.

“He’d won the Hardwicke at Royal Ascot in a similar fashion so we knew he was a bit special then, but he was remarkable on King George day. It’s always struck me how Olivier just knew after that piece of work that he’d win.

“He’s certainly well remembered here at Highclere, from our marketing material to beautiful bronzes by Charlie Langton.”

The race itself could hardly have gone any smoother, with Peslier sitting statuesque-like until two furlongs from home.

“The Derby winner had a pacemaker, Confront, and it was a very good piece of pacemaking, but I remember watching as they turned into the straight and Olivier hadn’t moved a muscle on him and he just exploded in the straight,” said Herbert.

“He went for a drugs test afterwards and I recall being told that his heart rate was almost immediately back to normal so he obviously had an unbelievable cardiovascular system.

“It was a performance that you could almost show someone with no interest in racing and they would immediately know it is something special, very rare.

“We are always looking for the next Harbinger and we thought we were going to win the King George a few years after with Telescope who also won the Hardwicke, but then John Gosden added his good filly Taghrooda at the last minute and she beat him!

“Moments like that King George day are absolutely what drive you forward. If I’m ever having a bad day I just go on YouTube and type in ‘Harbinger, King George 2010’.”

Herbert is also linked to another famous King George, perhaps the most famous of them all, in fact – the 1975 Grundy v Bustino battle.

“I remember Major Dick Hern (Bustino’s trainer) and my father (Lord Carnarvon) having dinner one evening and there was all this chat about two pacemakers and it was fascinating to hear. Then to see it all put into action, it was one of the greatest races of all time.

“Montjeu was another one I remember vividly, he never came off the bridle in winning and then showed his character by not wanting to go in the winner’s enclosure.

“It’s a great race, it always is, moments you never forget, and the search continues for us to find another Harbinger.”