The vizier al-Afdal put al-Musta'li on the Fatimid throne in 1094 over his elder brother Nizar, and the Ismailis split

Al-Mustansir, the eighth Fatimid imam-caliph, died in Cairo on 29 December 1094. Nizari tradition holds that he had designated his eldest son, Nizar. The vizier al-Afdal favoured the youngest son, Ahmad, who was married to al-Afdal's sister, and quickly secured the allegiance of the court for him as al-Musta'li. Nizar refused homage, said a written document named him heir, and fled to Alexandria. The governor, Nasr al-Dawla Aftakin, backed him. Nizar took the title al-Mustafa li-Din Allah, and a gold dinar struck in his name at Alexandria in 1095 was found in 1994. Al-Afdal's first assault in February 1095 failed. In November 1095 Nizar's commander left the city with much of the treasury, and Nizar and Aftakin surrendered on a promise of safety. In Cairo, Aftakin was executed and Nizar was walled up and died. In 1122 the caliph al-Amir issued a letter against Nizar's claim that still admitted Nizar had been officially proclaimed heir. The Ismailis divided. The Musta'li line stayed with Cairo. In Iran, Hasan-i Sabbah recognised Nizar, and Alamut struck coins in Nizar's name until 1162. The Nizari line of imams continues. On 5 February 2025, after the will of Aga Khan IV was unsealed in Lisbon, his son Rahim was named the 50th hereditary imam.