Queen Elizabeth's 2013 Ascot Gold Cup heroine Estimate has tested positive for morphine, Buckingham Palace announced yesterday.

Michael Stoute's five-year-old mare produced one of the iconic stories of last season when triumphing in the two-and-a-half-mile feature Group One at Royal Ascot and went down on her sword when narrowly denied by Leading Light in defence of her crown last month.

The British Horseracing Authority announced last week that five horses under the care of various trainers have been reported to show the presence of morphine in their 'A' samples, a prohibited substance on raceday under the Rules.

Initial indications are that the positive test taken from Estimate resulted from the consumption of a contaminated feed product, the Palace said.

A statement by John Warren, the queen's bloodstock and racing advisor, said: "On Thursday July 17th the British Horseracing Authority (BHA) announced that a number of post-race samples, obtained from recent race meetings, had been found to indicate the presence of morphine, which is a prohibited substance on race days. Five horses, under the care of various trainers, were affected.

"I can confirm that one of those horses was Estimate, the five year-old filly trained by Sir Michael Stoute and owned by The Queen. Initial indications are that the positive test resulted from the consumption of a contaminated feed product."

Publicised case

Morphine is banned by the

BHA

as it can be used to numb pain. Previously the most publicised case of a horse testing positive for morphine was Be My Royal after he had won the 2002 Gold Cup at Newbury.

He was subsequently disqualified and his trainer Willie Mullins was not fined but ordered to pay £5,000 (€6,340) in legal costs after a court case as he proved that the traces of morphine came from contaminated feed.