Sima Jiong became suspicious of Sima Yong the Prince of Hejian—because Sima Yong had initially wanted to support Sima Lun, until he saw that Sima Lun's cause was hopeless. Sima Yong knew of Sima Jiong's suspicion, and started a conspiracy; he invited Sima Ai the Prince of Changsha to overthrow Sima Jiong, believing that Sima Ai would fail; his plan was then to start a war against Sima Jiong in conjunction with Sima Ying. Once they were victorious, he would depose Emperor Hui and make Sima Ying the emperor, and then serve as Sima Ying's prime minister. In winter 302, Sima Yong declared his rebellion, and Sima Ying soon joined, despite opposition from his strategist Lu Zhi (). Hearing that Sima Ai was part of the conspiracy as well, Sima Jiong made a preemptive strike against Sima Ai, but Sima Ai was prepared and entered the palace to control Emperor Hui. After a street battle, Sima Jiong's forces collapsed, and he was executed. Sima Ai became the effective regent, but in order to reduce opposition, he submitted all important matters to Sima Ying, still stationed at Yecheng.