The Queen has been informed of her racehorse's failed drugs test, her majesty's racing advisor said.
Estimate, which won the Gold Cup at Royal Ascot in 2013, tested positive for morphine - a prohibited substance.
Sir Michael Stoute, the racehorse's trainer, is offering his "full co-operation" to the investigation, John Warren, from the Queen's bloodstock and racing advisor, said.
"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.
"Her Majesty has been informed of the situation."
More top news
Magician Richard Jones has won Britain's Got Talent 2016 after wowing the public with his amazing magic acts.
A medical tribunal found Dr Mark Bonar posed a "potential future risk of harm to patients".
After a lively start to the long weekend with torrential, thundery downpours - a drier night.