During Gao Cheng's Regency
In light of Gao Huan's death, the general Hou Jing, who did not respect Gao Cheng, first surrendered the 13 provinces he controlled (the region between the Huai River and Yellow River to Western Wei, and then to Liang. Gao Cheng's general Murong Shaozong (慕容紹宗), however, defeated both Xiao Yuanming – nephew of Liang's Emperor Wu, whom Emperor Wu sent to assist Hou – and Hou, capturing Xiao Yuanming and forcing Hou to flee to Liang. By 548, all but four provinces (which Western Wei took) were back under Eastern Wei control, and by 549, Eastern Wei had recaptured those provinces as well, after Gao Cheng captured Changshe (長社, in modern Xuchang, Henan).
Meanwhile, during the campaign against Hou, a conflict between Gao Cheng and Emperor Xiaojing would erupt. Gao Cheng was not as respectful to Emperor Xiaojing as Gao Huan was, and he ordered Cui Jishu to intensify his surveillance of Emperor Xiaojing. On one occasion, when Gao Cheng was attending a feast, he flashed a cup before Emperor Xiaojing as a toast – a very disrespectful gesture, as a subordinate, when toasting the emperor, was supposed to kneel. Emperor Xiaojing became angry, and remarked, "There is no such thing as an everlasting empire. Zhen do not necessarily treasure my life!" Gao Cheng angrily responded, "Zhen, zhen, zhen! You are a zhen with dog feet!" He ordered Cui to punch Emperor Xiaojing three times, and then left abruptly. Emperor Xiaojing thereafter entered into a conspiracy with his teacher Xun Ji (荀濟), Yuan Jin (元瑾), Liu Siyi (劉思逸), Yuan Daqi (元大器) the Prince of Huashan, Yuan Xuanhong (元宣洪) the Prince of Huainan, and Yuan Hui (元徽) the Prince of Jibei to consider overthrowing Gao Cheng. They dug a tunnel from within the palace to the outside of the city, intending to create a secret passage for imperial guards to go through, but the tunnel was discovered, and Gao Cheng entered the palace with his troops, arresting Emperor Xiaojing, putting him under house arrest, and executing the other members of the conspiracy.
In spring 549, Emperor Xiaojing was forced to create Gao Cheng the greater title of Prince of Qi, and give him the honorific office of Xiangguo (相國), both signifying a move toward Gao's taking of the throne. Gao Cheng formally declined these honors, and further made a formal request for Emperor Xiaojing to create a son as crown prince. Subsequently, in fall 549, Emperor Xiaojing created his son Yuan Zhangren (元長仁) crown prince. (It is not known whether Yuan Zhangren's mother was Empress Gao.)
Also in fall 549, Gao Cheng was meeting Chen Yuankang (陳元康), Yang Yin, and Cui Jishu, to secretly discuss the timeframe in which to take the throne, when his servant Lan Jing (蘭京) – a son of the Liang general Lan Qin (蘭欽) Gao Cheng captured in battle, and whom Gao Cheng had repeatedly threatened to kill – assassinated Gao Cheng and Chen. Gao Cheng's brother Gao Yang the Duke of Taiyuan, who was also in Yecheng at the time, killed Lan Jing and his associates, and publicly declared only that Gao Cheng had been wounded. Emperor Xiaojing, however, believed that Gao Cheng was dead, and secretly made the remark, "It is heaven's will that the Grand Marshall is dead. The power to rule should return to the imperial clan."
Read more about this topic: Emperor Xiaojing Of Eastern Wei