Trainer Sir Michael Stoute's five-year-old mare, who finished second in this year's race in June, is one of five horses reported to show the presence of morphine in their 'A' samples.
Queen's horse Estimate tests positive for morphine
The Queen's 2013 Ascot Gold Cup winner Estimate has tested positive for morphine, Buckingham Palace said on Tuesday.
According to the Palace, Estimate's positive test came due to the consumption of a contaminated feed product.
John Warren, the Queen's bloodstock and racing advisor, confirmed the news and said investigations were underway.
"On Thursday July 17 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.
"Sir Michael is working closely with the feed company involved to discover how the product may have become contaminated prior to delivery to his stables.
"As the BHA investigates this matter, including potential links between the different cases, Sir Michael continues to offer his full co-operation.
"There will be no further comment until the BHA announces its considered findings.
"Her Majesty has been informed of the situation."
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