Godolphin trainer Mahmood Al Zarooni is to attend a British Horseracing Authority disciplinary inquiry after prohibited substances were found in samples taken from 11 horses at his stables in Newmarket, England.
Godolphin racing manager Simon Crisford described it as "a dark day for Godolphin."
"We are all shocked by what has happened," he said.
Godolphin confirmed late Monday on its corporate website, godolphin.com , that Al Zarooni had admitted making a "catastrophic error."
Al Zarooni has trained some high-profile winners, including Monterosso in the 2012 Dubai World Cup — the world's richest horse race — since joining the racing organization of UAE Vice President, Prime Minister and Ruler of Dubai HH Sheikh Mohammed bin Rashid al Maktoum. 
"I deeply regret what has happened. I have made a catastrophic error," he said in a statement. "Because the horses involved were not racing at the time, I did not realise that what I was doing was in breach of the rules of racing. I can only apologise for the damage this will cause to Godolphin and to racing generally."
Crisford said Sheikh Mohammed was "absolutely appalled when he was told and this is completely unacceptable to him."
"Sheikh Mohammed has instructed me to begin an urgent review of all of our procedures and controls," Crisford said. "That is already underway and we will take advice from the BHA in completing it."
All horses which returned positive tests will be barred from racing at least until the BHA inquiry is finished.
The British Press Association reported that the BHA obtained samples on April 9 from 45 horses trained by Al Zarooni at Moulton Paddocks stables and Horseracing Forensic Laboratory analysis showed that 11 of the samples contained traces of prohibited substances, including ethylestranol and stanozolol.
Adam Brickell, Director of Integrity, Legal and Risk for the BHA, said ethylestranol and stanozolol are anabolic steroids that are prohibited under British Rules of Racing either in training or racing.
He said a disciplinary panel inquiry would take place as soon as possible.
"The BHA understands the importance of this process being carried out as quickly as possible because of implications for betting markets," he was quoted as saying.
Should Dubai's Sheikh rein it in? Maybe it's time for a new hobby for the horse-loving ruler? Do you think its time the Gulf race scene was cleaned up after at least 2 instances of horses testing positive for substances?