British mystery: Who doped the Queen's horse?

LONDON (AP) -- 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 substance morphine.

Buckingham Palace says that early indications suggest that the five-year-old filly, Estimate, consumed the substance as a result of contaminated feed.

Britain's Queen Elizabeth II, left, with her daughter Princess Anne greet her horse Estimate, who won the Gold Cup horse race on the third day of the 2013 Royal Ascot horse race meeting, traditionally known as Ladies Day, in Ascot, England. (AP Photo/Alastair Grant, file)

John Warren, the queen's bloodstock and racing adviser, said Tuesday 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.

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