The ruler of Dubai is being investigated by equestrian authorities after a horse he owns and rides failed drug tests after two races.

Sheik Mohammed said he was unaware of the drugs but accepts full responsibility. The drug use came to light following testing by his staff after endurance races this year in Bahrain and Dubai.

The Federation Equestre Internationale (FEI) said April 7 it is investigating. The federation’s president is Princess Haya of Jordan, who is married to Sheik Mohammed.

She has led a campaign for a drug-free sport and will step aside from her official duties when the governing body considers the case. Her husband is one of the world’s leading breeders and owners of Thoroughbred race horses