Hamdan Bin Mohammad Bin Rashid Al Maktoum, the Crown Prince of Dubai and a son of Princess Haya's husband Sheik Mohammed bin Rashid al Maktoum, was the rider of Eo Fawati, who has tested positive after a 120km race in Bahrain in January.
Eo Fawati tested positive for 16-b Hydroxy-Stanozolol, a metabolite of stanozolol and a synthetic anabolic steroid.
In January and February Tahhan, a horse ridden by Princess Haya's husband tested positive to 16-b Hydroxy-Stanozolol and Guanabenz after 120km rides in Bahrain and Dubai. Guanabenz is used to treat high blood pressure in humans. In horses, it is used to reduce the incidence or severity of exercise induced pulmonary hemorrhage (EIPH). Hydroxy-Stanozolol is a metabolite of Stanozolol, a synthetic anabolic steroid.
For both cases Princess Haya has stepped aside and the FEI's second vice-president, Chris Hodson, will take over her duties.
The two men face suspension for the offences, which will go before the FEI's seven-member tribunal.
Princess Haya has been a vocal opponent of horse doping, and has vowed to clean up equestrian sport.