Oman’s Sultan Qaboos bin Said dies at the age of 79 after around half a century at the helm of the state amid a battle with resurgent colorectal cancer.

The head of state passed on Friday evening, Reuters reported, citing state media.

Muscat subsequently declared a three-day period of national mourning.

Recently, reports had suggested that the sultanate was preparing for an elaborate succession process as Qaboos’ health was not taking any turn for the better.

Qaboos had traveled to Belgium last December to seek medical treatment.

He absented himself from an annual Persian Gulf Cooperation Council summit in Saudi Arabia in the same month, giving rise to speculations about his failing constitution.

Sultan Qaboos rose to power in the former British protectorate in a 1970 coup that was assisted by London.

He had no children and had not publicly appointed a successor.

The sultanate’s court now has to pick a replacement in three days. The sultan has already named his desired successor but has kept his identity secret to avoid political fallout.

Should the court fail to name the next sultan, the authorities will have to open secret letters, in which Qaboos has penned the name of the heir to the throne.

The task of opening the envelopes has to be performed jointly by the nation’s defense council, the head of the Supreme Court, and the heads of the two chambers of the consultative council.

Oman brokered conflict resolution negotiations among many regional states under Qaboos.

The sultanate, however, notoriously hosted Israel’s Prime Minister Benjamin Netanyahu in 2018 amid vocal cautions against attempts at bringing the regional Arab states and the regime close.