Before Empress Yang Yan died in August 274, she was fearful that whoever became empress next would undermine her developmentally disabled son Crown Prince Zhong's position as crown prince, and therefore she asked Emperor Wu to marry her cousin Yang Zhi after her death.
Emperor Wu agreed and, in December 276, married Yang Zhi and created her empress.
In 289, Emperor Wu grew ill, and considered whom to make regent for Crown Prince Zhong.
Yang Jun quickly showed himself to be autocratic and incompetent, drawing the ire of many other nobles and officials.
He knew Emperor Hui's empress Jia Nanfeng to be strong-willed and treacherous, so he tried to put people loyal to him in charge of all the defense forces of the capital Luoyang, and also ordered that all edicts not only be signed by the emperor but also by Empress Dowager Yang before they could be promulgated.
In 291, after Sima Wei returned to Luoyang from his defense post (Jing Province (荊州, modern Hubei and Hunan)) with his troops, a coup went into progress in April.
Empress Jia, who had her husband easily under her control, had him issue an edict declaring that Yang Jun had committed crimes and should be removed from his posts.
Initially, her closest servants were allowed to remain to serve her, but in February 292, Empress Jia had them moved elsewhere.