Lun then requested a high level office, but was rebuffed by Empress Jia's advisors Zhang Hua and Pei Wei (裴頠). After Empress Jia, in jealousy, deposed the crown prince Sima Yu (born not of her but of her husband's concubine Consort Xie Jiu. In 299, there was a conspiracy to overthrow her and restore the crown prince. Sima Lun was persuaded to join the conspiracy, but Lun had another plan for him: instead encourage Empress Jia to assassinate the crown prince in exile, and then use the assassination as the excuse to overthrow her. Sima Lun accepted the plan and persuaded her to assassinate the crown prince, which she did in 300. He then declared a coup against her and arrested her, slaughtering her clan and her associates (including Zhang and Pei). He then forced her to commit suicide. Sima Lun then became regent for the developmentally disabled Emperor Hui, but was described to be not particularly more intelligent than Emperor Hui. Even though he carried the regent title, true power was in Sun Xiu's hands. Under Sun Xiu's persuasion, he deposed Emperor Hui and declared himself emperor in 301, offering Emperor Hui the honorific title of retired emperor but putting him under house arrest. Emperor Hui's grandson, the crown prince Sima Zang (司馬臧), was executed. The act of usurpation brought widespread anger. In order to appease those who might be angry at his usurpation, Sima Lun rewarded many people with honors. Sun, in particular, was issuing edicts based on his own whims. Suspecting three autonomous key princes—Sima Jiong the Prince of Qi (Emperor Hui's cousin and the son of Emperor Hui's uncle, Prince You of Qi), Sima Ying the Prince of Chengdu (Emperor Hui's brother), and Sima Yong the Prince of Hejian (the grandson of Emperor Hui's great-granduncle Sima Fu the Prince of Anping), each of whom had strong independent military commands—Sun sent his trusted subordinates to be their assistants. Prince Jiong refused and declared a rebellion to restore Emperor Hui. Prince Ying, Sima Ai the Prince of Changshan (Emperor Hui's brother), and Sima Xin (司馬歆) the Duke of Xinye (the son of a granduncle of Emperor Hui) all declared support for Prince Jiong.