During the reign of the thirteenth Sultan Muhammad Ali, there was a disagreement between the son of the Sultan, Pengiran Muda Bongsu and Pengiran Muda Alam, the son of PengiranAbdul Mubin over the results of a cockfight which Pengiran Muda Bungsu lost. His defeat was jeered by Pengiran Muda Alam. In his rage, Bongsu killed Pengiran Muda Alam and escaped from the scene. In revenge, Abdul Mubin and his followers garroted Sultan Muhammad Ali. Abdul Mubin then made himself the fourteenth Sultan and took the title of "Sultan Hakkul Abdul Mubin". He tried to appease the previous Sultan's followers by appointing Muhammad Ali's grandson, Muhyiddin as the new Bendahara. After a while, however, Muhammad Ali's supporters took revenge by convincing Bendahara Muhyiddin to stand up against Abdul Mubin. Bendahara Muhyddin initially refused, but then later agreed to do so. His supporters started making disturbances in the form of poking spears into palaces and homes. Sultan Abdul Hakkul Mubin then moved his palace to Chermin Island under the advice of Muhyiddin with the intent to wait the crisis out. After he left, however, Muhyiddin declared himself the fifteenth sultan. A battle between the two competing Sultans then ensued. Thus, the civil war of Brunei started.
Fighting and outcome
During the Civil War, Abdul Mubin fled to Kinarut where, he stayed there for ten years, repelling repeated attacks by Sultan Muhyiddin. They returned to Brunei after a final attack by Muhyiddin's forces in which they failed to defeat Abdul Mubin. Muhyiddin was concerned that the civilwar was dragging on too long and asked the help of the sultan of Sulu to send forces. He reportedly promised the land of eastern Sabah as a reward for the Sulu's assistance. Muhyiddin eventually emerged victorious. Abdul Mubin was killed in the civil war. It is not clear to historians whether Muhyiddin asked for Sulu’s help in the civil war. The Sultan of Sulu at that time on his part, however, claimed that he was asked by Brunei to help and was promised eastern Sabah as a reward. As promised, the Sultan of Sulu received eastern Sabah as an honorary gift from the Sultan of Brunei, for the Tausugs' help during the civil war.
