Sheikh Rashid bin Mohammed bin Rashid Al Maktoum.

Sheikh Rashid bin Mohammed bin Rashid Al Maktoum, a son of Dubai’s ruler and elder brother to the emirate’s heir apparent, has died at age 33.

The United Arab Emirates state news agency WAM said Saturday that he died of a heart attack.

Sheikh Rashid was the first son of Sheikh Mohammed bin Rashid Al Maktoum and his senior wife, Sheikha Hind bint Maktoum bin Juma Al Maktoum. In addition to his role as Dubai ruler, Sheikh Mohammed is vice president and prime minister of the UAE.

Sheikh Rashid was an avid sportsman and horse racing enthusiast. His younger brother Sheikh Hamdan is Dubai’s crown prince.

The commercial hub of Dubai is one of seven sheikhdoms that comprise the Emirates federation. The ruler’s court has declared three days of mourning.