Generation.
After the death of Emperor Tongzhi, because he had no son or adoptive son, the unopinionated Empress Dowager Ci'an (Empress Dowager of the East) and the ambitious Empress Dowager Cixi (Empress Dowager of the West) jointly agreed that Prince Chun (Yi-)'s second son Zai- should be the successor son of Emperor Xianfeng and inherit the throne. This was Emperor Guangxu. According to the throne succession law of the Qing Dynasty, this is unreasonable, because Tongzhi and Guangxu are both generations with the character "Zai". They are cousins, and there is no precedent in the Manchu Qing Dynasty. However, Guangxu's father Yi - was the brother of Emperor Xianfeng, and Guangxu's mother was the sister of the Queen Mother of the West. The two brothers married two sisters. The Queen Mother of the West was both Guangxu's eldest aunt and Guangxu's eldest aunt.