Estimate, the racehorse which has tested positive for a banned substance, helped make sporting history for the Queen as she became the first reigning monarch to win Royal Ascot's Gold Cup.
The Queen was pictured beaming as Estimate crossed the line in first place during the dramatic race last year.
Prime Minister David Cameron congratulated the Queen in a tweet saying: ''Huge congratulations to Her Majesty for Estimate's victory at Royal Ascot - first time ever a reigning monarch's horse has won the Gold Cup.''
Her Majesty won £155,960 in prize money after Estimate's victory.
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