A racehorse owned by the Queen and trained by Newmarket based Sir Michael Stoute has tested positive for a banned substance.
In a statement the Queen's racing advisor says it may have been caused by contaminated feed.
Four more horses from different trainers also tested positive.
Estimate, the racehorse owned by the Queen, helped her to make sporting history as she became the first reigning monarch to win Royal Ascot's Gold Cup.
"On Thursday 17 July the British Horseracing Authority announced that a number of post-race samples, obtained from recent race meetings, had been found to indicate the presence of morphine, which is a prohibited substance on race days. Five horses, under the care of various trainers, were affected.
I can confirm that one of those horses was Estimate, the five-year-old mare trained by Sir Michael Stoute and owned by the Queen. Initial indications are that the positive test resulted from the consumption of a contaminated feed product. 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."
More top news
Heavy showers will continue in places overnight and it will feel muggy. Tomorrow, showers clear early on and it will be a sunny day.
A transformation from gravel pits to grebe habitat, a quarry in Cambridgeshire that's slowly being turned into Britain's biggest reed bed.
Student Deryn Blackwell is celebrating exam success after battling two deadly cancers and enduring four bone marrow transplants