Queen Elizabeth's racehorse tests positive for banned painkiller morphine

A racehorse owned by Britain's Queen Elizabeth II that won the prestigious Gold Cup at Royal Ascot last year has tested positive for the banned painkiller, morphine.

5-year-old filly 'Estimate' won the prestigious Gold Cup at Royal Ascot last year

Queen Elizabeth's five-year-old filly Estimate has tested positive for a banned substance, morphine. (Alastair Grant/Associated Press)

A racehorse owned by Britain's Queen Elizabeth II that won the prestigious Gold Cup at Royal Ascot last year has tested positive for the banned painkiller, morphine.

The British Horseracing Authority announced last week that tests on five horses under the care of various trainers showed the presence of morphine in their `A' samples.

On Tuesday, the queen's bloodstock and racing adviser, John Warren, said that the monarch's five-year-old filly Estimate was one of the five.

Buckingham Palace said that early indications suggest that Estimate consumed the substance as a result of contaminated feed.

Warren said in a statement that Estimate's trainer Michael Stoute "is working closely with the feed company involved to discover how the product may have become contaminated prior to delivery to his stables."

Estimate finished second in this year's Gold Cup behind Leading Light.

Warren added: "Her Majesty has been informed of the situation."

Previously, Britain's most publicized case of a horse testing positive for morphine was Be My Royal after he had won the 2002 Hennessy Gold Cup at Newbury. The horse was subsequently disqualified.