Tang Gaozu's second son, Li Shimin, was born with his eldest brother Cheng Jian, his third brother Yuan Ba and his fourth brother Yuan Ji, and was his first wife. Yuan Ba died early, and Cheng Jian and Yuan Ji also took part in the war to conquer the Central Plains in the early Tang Dynasty, but their contributions and expectations were not as good as those of the people. After Li Yuan proclaimed himself emperor, he became a prince, and Yuanji was closely related to him, causing estrangement and suspicion between the two sides. The gap between Li Shimin and the eldest brother and the fourth brother Yuanji involves such a background. He made friends with courtiers himself, and later accused his brother of murdering him with "being a villain outside, being lucky inside", which can be found in Old Tang Book (which is close to the official history according to the documents of the Five Dynasties Tang Dynasty). The Book of the New Tang Dynasty was written in the Song Dynasty. In fact, he and his entourage ambushed in Xuanwu Gate and murdered Cheng Jian and Yuanji. When it was completed, Shimin personally drew a bow and shot an arrow, while Yuanji died in his hands. But on the day of burial, "Taizong was in Yiqiumen, crying very sadly." Cheng Jian and Yuan Ji each had five people, and when this happened, Taizong was only 28 years old. His 10 nephews are not described in detail in the history books. They may still be children. Two months later, Tang Gaozu abdicated as the emperor's father, and Li Shimin was located in the East Palace.