Duke of Marmalade sired four European Classic winners in 2015, namely Nutan, Star of Seville, Simple Verse and Sound of Freedom.

[1] Duke of Marmalade was one of the last crop of foals sired by Danehill one of the most successful stallions of the last twenty years, producing the winners of more than a thousand races, including one hundred and fifty-six at Group One/Grade I level.

Ridden by Seamie Heffernan and starting at odds of 11/4 (2.75-1) favourite, he was towards the back of the field in the early stages before making progress in the last two furlongs to finish second to Chanting.

Michael Kinane tried to lead all the way on the colt-and was still in front inside the final furlong-before being caught and beaten a neck by Jamie Spencer on his stable companion Excellent Art, with another O'Brien-trained runner, Astronomer Royal in third, and Cockney Rebel in fifth.

He ran up to his best form in a highly competitive race to finish fourth behind the Derby winner Authorized, Dylan Thomas and Notnowcato.

At the Curragh a month later, he justified odds of 1/3 (0.33-1) in the Tattersalls Gold Cup, being driven out by Murtagh[30] to beat the filly Finsceal Beo by one and a quarter lengths.

[31] In the Prince of Wales's Stakes at Royal Ascot he produced what his trainer considered his best performance to date,[32] taking over from Red Rock Canyon in the straight where he "stormed clear" to win by four lengths from Phoenix Tower.

[34] He then stepped up to twelve furlongs for Britain's most prestigious[35] weight-for-age race, the King George VI and Queen Elizabeth Stakes, for which he was made 4/6 (0.67-1) favourite.

[36] Duke of Marmalade was settled by Murtagh in the middle of the field before being switched to the outside in the straight and overtaking Red Rock Canyon entering the final furlong.

He was immediately challenged and headed by the Michael Stoute-trained Papal Bull but "rallied gamely" to regain the lead close to the finish and win by a half a length.

While pacemakers are allowed,[40] it is considered unfair to provide additional assistance, for instance manoeuvring a horse to ensure a clear run for a stable companion.

"[42] It was expected that Duke of Marmalade would meet New Approach again in the Irish Champion Stakes in September,[43] but following heavy rain in the build-up to the race O'Brien withdrew the colt, saying "we don't want to subject him to soft ground now, with the rest of the year in mind.

[45] He was settled on the outside, but when Murtagh attempted to have him move forward in the straight, he made no progress and finished seventh of the sixteen runners behind Zarkava.

Racing on a synthetic track for the first time, he ran in third place for much of the distance and briefly headed the field turning into the straight, but faded in the closing stages to finish ninth of the twelve runners behind Raven's Pass.

[47] Murtagh and O'Brien characterised the performance as typifying "the end of a long, hard season" and Duke of Marmalade's retirement was announced immediately.

"[53] He was retired from racing at the end of 2008 and stood as a stallion for Coolmore Stud where he used to shuttle between their main base in County Tipperary, Ireland during the Northern Hemisphere breeding season and Coolmore's Australian stud farm in the Hunter Region, New South Wales, during the Southern Hemisphere breeding season.

[55] In October it was announced that Duke of Marmalade had been pensioned from stud duty due on veterinary advice but would remain at Drakenstein.