Chaucer all the rage for Epsom
A son of the late Montjeu, he won both his starts at two before reappearing in what proved to be a dramatic renewal of the Derrinstown Stud Derby Trial at Leopardstown.
Not suited by a race that essentially turned into a sprint and ultimately saw first-past-the-post Ebanoran demoted to second behind Fascinating Rock, O'Brien's charge was not disgraced in third, beaten two and three-quarter lengths.
Hills cut his price for Epsom on June 7 to 8-1, having been 10-1 and 12-1. Ladbrokes went 7-1 from 12-1.
His stablemate Australia remains the 4-6 favourite with Hills, and 4-5 at Ladbrokes.
William Hill spokesman Jon Ivan-Duke said: "Large bets on Ballydoyle inmates aren't uncommon, but given this is a sizeable bet against the favourite, it's really captured our attention."
In a market without Australia, Hills make Geoffrey Chaucer the 4-1 favourite, while Ladbrokes go 11-4 (from 4-1).
Alex Donohue of Ladbrokes said: "The 'without Australia' market was a wide-open heat until recently but punters have moved decisively to make Geoffrey Chaucer favourite.
"The latest shake-up in both markets suggests he'll be the runner to give hot favourite Australia the most to think about on the day."
Reflecting on Geoffrey Chaucer's Leopardstown return at Ballydoyle press day earlier this month, O'Brien said: "They walked first of all at and then it was bumping cars in the straight. It was just a pity.
"You're happy enough when you get beat if you learn something but nobody learned anything.
"We are very happy with him. He's doing everything very well.
"There was plenty of hustle and bustle and he won't get that at Epsom."