There are several reasons. Yi Xin, the first Prince Gong, was a very powerful man. He will not succumb to the rule of Empress Dowager Cixi. In other words, Yixin and Cixi are only cooperative relations, not master-servant relations. After the coup with Cixi, the second prince Yixin became the deliberative king, and further expanded his power, threatening the rule of Cixi. The third is that Prince Gong is ambitious. He was not satisfied with just being the king of deliberation, and was embarrassed with Empress Dowager Cixi everywhere. Fourth, Prince Gong was bent on killing An Dehai, the eunuch favored by Cixi. Therefore, Cixi hates Prince Gong more and more, and the power of Prince Gong is best to be overhead by Cixi step by step. Cixi is the famous Empress Dowager of Qing Dynasty and the concubine of Emperor Xianfeng. Emperor Tongzhi is the child of Cixi and Emperor Xianfeng. When Emperor Xianfeng was in power, his achievements were few. Later, when Xianfeng died, he passed the throne to his son Zai Chun, the later Tongzhi Emperor. He was only six years old when he succeeded to the throne. Emperor Xianfeng appointed Duan Hua and other ministers to assist Tongzhi before his death, but it didn't play much role. Because after Xianfeng's death, Empress Dowager Cixi cooperated with Prince Gong to launch a coup. Cixi also succeeded in becoming the actual supreme ruler, and even the emperor couldn't help it. Similarly, Prince Gong became the king of the proceedings with all his heart, with great power.
This is a successful cooperation between Prince Gong and Cixi. The basis of cooperation is that Cixi and Prince Gong share the same interests. Therefore, this does not mean that Empress Dowager Cixi and Prince Gong can live in harmony with one heart and one mind. After all, the palace is full of struggle and competition at any time. For their own interests, the contradiction between Prince Gong and Empress Dowager Cixi has become more and more obvious with the passage of time, and has reached an irreconcilable level.
On one occasion, Empress Dowager Cixi ignored the etiquette tradition and went out directly from the main entrance of the palace. You know, the main entrance is usually only accessible to the emperor. It happened that this scene was seen by Prince Gong, so Prince Gong stopped the minister, but the minister told Cixi about it. Cixi flew into a rage, thinking that Prince Gong was bent on doing so to lose face, and the contradiction between the two became more and more fierce. Finally, Cixi used her power to gradually exploit Yixin's power until Prince Gong Yixin died.