World's top rated horse status was confirmed for Harbinger on Monday when Phil Smith, the BHA head of handicapping, made the announcement he had been given the new mark of 135.
Harbinger's new rating is a 12lb increase on the figure handicappers in Britain had put on him before the King George VI and Queen Elizabeth Stakes, which he absolutely triumphed in track record time, and with a event record margin of 11 lengths.
"We looked at the second horse, Cape Blanco, and imagined what if Harbinger had not been in the race," Smith told At The Races.
"Cape Blanco was 119 going into the race and so we took the view that he had replicated his 119.
"We therefore just had to decide what we called the 11 lengths. We took the view that was worth 16lb which would be pretty much the norm and brings Harbinger out on 135. It is quite a big jump. We had him on 123 before that, but I am pretty confident he is that and could probably be better.
"It was very impressive. Instantly we have got Harbinger 1lb below Sea The Stars's end-of-season performance. Harbinger has still got one, two or possibly three more races to come, so we will see how the King George works out, see how Harbinger runs in his subsequent races. It may well be we have him as high or higher than Sea The Stars.
He added, "We would want him to do it again before we can get him into the late 130s or early 140s."