Aidan O'Brien believes a step back up in distance can help Hydrangea raise her game for the King George VI And Queen Elizabeth Stakes at Ascot.

The Ballydoyle maestro has saddled four previous winners of the midsummer highlight in Galileo (2001), Dylan Thomas (2007), Duke Of Marmalade (2008) and Highland Reel (2016).

It is fair to say O'Brien's hand is not as strong as in some years, with the defection of Kew Gardens a significant blow.

However, Hydrangea is already a Group One winner over the course and distance, having landed the Qipco British Champions Fillies & Mares Stakes last October, and O'Brien is hopeful she can bounce back from a disappointing effort over a mile in the Duke of Cambridge Stakes at Royal Ascot.

He said: "Hydrangea is in good form. She's had two runs (this season) and she's back up a mile and a half again.

"She got a mile and a half last year and maybe a mile is a bit tight for her now. We're looking forward to seeing what happens."

O'Brien has a second string to his bow in Rostropovich.

The son of Frankel filled the runner-up spot in the King Edward VII Stakes at the Royal meeting before going down by just half a length to Joseph O'Brien's Latrobe in the Irish Derby.

O'Brien added: "Rostropovich is in good form. He's a solid horse. He had a very good run in the Irish Derby, gets a mile and a half, handles quick ground and seems to be in good form since the Curragh.

"I think he has improved since stepping up in trip."

John Gosden claimed a third King George victory within the last seven years when star filly Enable trounced her rivals 12 months ago.

The Clarehaven handler has this year declared Cracksman and high-class filly Coronet, although the latter will only bid to bounce back from if underfoot conditions are deemed suitable, with connections keen to avoid fast ground following his defeat at Royal Ascot.

The Sylvester Kirk-trained Salouen got to within a head causing an almighty shock and beating Cracksman in the Coronation Cup at Epsom last month.

The four-year-old was last seen finishing third in the Grand Prix de Saint-Cloud and Kirk is happy to shoot for Group One glory again rather than lowering his stable star's sights.

Speaking ahead of another leg of the Qipco British Champions Series, the trainer said: "It gives the place a different feel when you've got a fellow like him knocking around. He gives everyone a lift and you could not wish for a horse who is more honest, genuine, consistent or easy to deal with.

"We keep aiming at the highest level and Saturday will be another big ask, but we'd rather take our chance at the top level again.

"It's frustrating not to have got his head in front for a while, but we'd probably only end up bumping into an improver if we dropped him in grade.

"He's consistent and if he puts his best foot forward he should again be there or thereabouts."

Rank outsider Desert Encounter, trained by David Simcock, completes the line-up.