He started favourite in an eight-runner field and won by two and a half lengths from Temps Libre after taking the lead 200 metres from the finish.

Four weeks later he started 3/5 favourite for the Prix de Lormoy at Longchamp Racecourse but after taking the lead in the straight he was overtaken in the last 100 metres and beaten a length by the outsider Silver Trail.

Despite his defeat, Flintshire was moved up in class to contest the Group III Prix du Lys over 2400 metres at Chantilly on 16 June and started the 7/2 second favourite behind the Élie Lellouche-trained Park Reel.

After racing towards the middle of the nine runner field he took the lead 200 metres from the finish and accelerated clear to win in "impressive" style by three lengths from Park Reel.

He started 5/4 in a strong field but although he made progress in the straight he never looked likely to win and finished fourth behind Kizuna, Ruler of the World and Ocavango.

On his first appearance as a four-year-old, Flintshire was sent to England to contest the Coronation Cup at Epsom Downs Racecourse on 7 June and finished second to the odds-on favourite Cirrus des Aigles with the unplaced runners including Talent and Joshua Tree.

Three weeks later, Flintshire started 13/8 favourite for the Grand Prix de Saint-Cloud and finished fifth of the seven runners behind the subsequently disqualified Spiritjim.

[9] Flintshire was scheduled to contest the King George VI and Queen Elizabeth Stakes at Ascot Racecourse in late July but was withdraw after running a high temperature shortly before the race.

The other beaten horses included Taghrooda, Kingston Hill, Harp Star, Just A Way, Ruler of the World, Al Kazeem, Avenir Certain, Gold Ship and Ectot.

In a slowly-run race, Guyon settled the colt in mid-division before moving forward on the outside in the straight, taking the lead inside the final furlong and winning by half a length from the locally trained Willie Cazals.

In the Sheema Classic at Meydan Racecourse on 28 March, Flintshire started 3/1 second favourite behind the Japanese filly Harp Star in a field which also included Dolniya, Main Sequence and Designs On Rome.

An intended run in the King George VI and Queen Elizabeth Stakes was abandoned owing to the soft ground at Ascot.

Flintshire was shipped back to America and contested the 1.5-mile (2,400 m) Sword Dancer Stakes at Saratoga Race Course in New York State on 29 August.

Flintshire attempted to repeat his 2014 success in the Hong Kong Vase and finished second to the Irish three-year-old Highland Reel.

On his first appearance for his new trainer, he contested the Grade I Manhattan Handicap at Belmont Park and started favourite in an eleven-runner field which included the 2015 American Champion Male Turf Horse, Big Blue Kitten.

To prevent a repetition of the problems experienced in the Bowling Green, Juddmonte also entered Inordinate as a "rabbit" to ensure a fast pace.

The other nine runners included Highland Reel (King George), Found (Arc, 2015 Breeders' Cup Turf), Ectot, Ashleyluvssugar (Del Mar Handicap), Da Big Hoss (American St. Leger Stakes), Mondialiste (Arlington Million), Ulysses (an improving three-year-old from Europe) and the veteran Twilight Eclipse (Man o' War Stakes).

Unexpectedly, Highland Reel took the lead soon after the start and set a steady pace before kicking seven lengths clear of his opponents at half way.

Flintshire made a late move but had too much ground to make up, finishing 1+3⁄4 lengths back, with Found staying on to take third place.