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
Heavy thundery rain for parts of Northern Ireland and Scotland
Four men are being interrogated in Spain's National Court over the vehicle attacks that killed 15 people and wounded more than 120 others.
In the position paper the Government sets out plans to ensure that cross-border legal disputes are dealt with in a "fair way" post-Brexit.