O'Brien is prepared to unleash his formidable arsenal on Friday

With Kyprios and Tower of London playing on Friday, Aidan O'Brien's preparations for the Gold Cup will become more apparent.

Kyprios, who was injured last year and was unable to add to his 2022 success in the race, is the clear favourite for the main event at Ascot.

He made a stunning comeback to the racing world last season, winning the Irish St Leger and Long Distance Cup on Champions Day, and then easily defeating the field at extreme odds in the Vintage Crop Stakes this past month.

In the meantime, Tower of London is the newest member of the staying division.

Fourth to stablemate Continuous in St Leger, he was the Irish Cesarewitch's defeated favourite but has proven to be a better performer by winning twice abroad.

He started the Red Sea Turf Handicap in Saudi Arabia by coming from an uncompromising position, and he went on to win the Dubai Gold Cup like a very fine horse by quickening up nicely.

Kyprios races the Saval Beg Levmoss Stakes at Leopardstown after taking the Vintage Crop, while Tower of London races the Boodles Yorkshire Cup on the Knavesmire, following O'Brien's well-trod path.

“We’ve been very happy with Tower Of London really,” said O’Brien. ”He’s progressing well. He ran a nice race in the St Leger but has shown in his last two races that he’s improving quickly. He did well to win in Saudi when he met some trouble, but then in Dubai what he did was really pleasing.”

Tower of London will be up against Willie Mullins' Vauban, which is making his first appearance since finishing second in the Melbourne Cup. Gregory, the winner of the Royal Ascot. Giavellotto, the race's winner a year ago, and Hamish and Naqeeb, both from William Haggas and owned by Karl Burke.

After being chased home by stablemate Queenstown in the Vintage Crop, Dawn Rising, Sunchart, Serious Challenge, and Yashin, Kyprios clashes with them.