Investec Coronation Cup 2017 – Brothers Highland Reel and Idaho lock horns at Epsom on Friday

Highland Reel sets the standard having already struck four times at the highest level on three different continents.

The year-younger Idaho won the Great Voltigeur at York last summer, but unseated his rider when an odds-on favourite to claim Classic glory in the St Leger at Doncaster.

O'Brien said: "We've always thought Idaho would get to the same level as Highland Reel. Physically, maybe he is a bit bigger and stronger than him.

"Things have not always fallen for him - unusual things have happened, like what happened in the Leger.

"We think he is progressing all the time and will progress through the year."

John Gosden, who has never won the Coronation Cup, sends his top-class filly Journey into action.

She rounded off last season with three consecutive victories and completed a hat-trick with an emphatic success in the Qipco British Champions Fillies & Mares Stakes at Ascot.

Gosden said: "We've been pointing her towards this race for some time and she worked nicely on Sunday.

"We are very happy with her, but I think she will come on a lot for the race.

"It looks a good version of the race and she will appreciate any rain that comes.

"She handles most ground, but I think she enjoys a little bit of give.

"Track-wise, we will find out on the day. You don't really know how they are going to handle it until they race around there."

Godolphin trainer Charlie Appleby is double-handed with last summer's Coral-Eclipse hero Hawkbill and progressive stable companion Frontiersman.

Hawkbill opened his account for the season in a Group 3 at Newbury a fortnight ago, while Frontiersman won with plenty in hand in a Newmarket handicap on his latest appearance.

The latter did, however, miss an engagement at York on Saturday due to heat in a leg.

"We've declared the pair of them and as long as it's genuine good ground, all being well, Hawkbill will take his chance," said Appleby.

"If it dried out more than people are expecting, we might have to have a rethink, but he's been in good form since Newbury and if conditions are right he's capable of running a big race.

"It's obviously a big step up for Frontiersman, but he's working really well at home.

"If he translates what he's doing on a morning to the race he could be bang there."

Sheikh Mohammed is also represented by the Saeed bin Suroor-trained Prize Money, who beat Postponed at Meydan earlier in the year and was last seen finishing fourth in the Dubai Sheema Classic.

Bin Suroor told www.godolphin.com: "Prize Money ran some very good races out in Dubai, winning the Dubai City of Gold.

"We took him to Chelmsford City for a piece of work last Saturday, which went well, and he is ready to start his European campaign.

"He looks in good condition and a mile and a half is a nice trip. He is a horse that we like and it is a case of so far, so good with him."

Ralph Beckett's Air Pilot, the Ed Dunlop-trained Red Verdon and Elbereth from Andrew Balding's stable complete the line-up.