Kuwaiti Emir Sheikh Sabah Al-Ahmed Al-Sabah underwent a “successful surgery” Sunday morning, state-run Kuwait News Agency reported.

The 91-year-old ruler had been admitted to hospital on Saturday for medical tests.

Read: Kuwait’s Emir in hospital for checkups, Crown Prince to assume some duties

An Emiri order has been issued for the Crown Prince Sheikh Nawaf Al-Ahmed Al-Sabah to temporarily assume some of the constitutional functions and duties performed by the emir, according to a minister of the Emiri Diwan, or royal court.