 After the eighteenth Imam, al-Mustansir Billah, the Nizari sect believed that his son Nizar was his successor, while another Ismāʿīlī branch known as the Mustaali (from whom the Dawoodi Bohra would eventually form), supported his other son, al-Musta'li.The Fatimid dynasty continued with al-Musta'li as both Imam and Caliph, and that joint position held until the 20th Imam, Al-Amir bi-Ahkami'l-Lah (1132 CE).At the death of 20th Imam Amir, one branch of the Mustaali faith claimed that he had transferred the Imamate to his son At-Tayyib Abu'l-Qasim, who was then two years old.