Prince Rahim al-Hussaini, the son of Aga Khan IV, was named his successor on Wednesday. He will inherit the role of the spiritual leader of millions of Ismaili Muslims around the world.

The late Aga Khan IV, 88 — a billionaire known for his entrepreneurship and philanthropy — died on Tuesday. Prince Rahim was named as his successor after the unsealing of his will, according to the Aga Khan Development Network.

Read more: King Charles Mourns the Death of Aga Khan IV.

Prince Rahim, who is the Aga Khan V, will take the reins of a Shiite Muslim lineage that claims descent from the Prophet Muhammad. Ismaili Muslims, numbering 12 million to 15 million, live in more than 35 countries including Syria, Afghanistan, Pakistan and Tajikistan.

His family and the Ismaili institutions are stunningly wealthy: estimates of the fortune have ranged from $1 billion to $13 billion, with diverse holdings ranging from airlines, racehorses to newspapers.