After Tang Dynasty founder Emperor Gaozu named his son Li Jiancheng the crown prince, an intense rivalry developed between him and his younger brother, Li Shimin. Each prince was advised by his staff members to act first against the other, and, in 626, believing that Li Jiancheng was plotting to kill him, Li Shimin ambushed and killed the crown prince and another brother of theirs at Xuanwu Gate, which led to Emperor Gaozu's palace. What did the emperor do when he learned of his sons' deaths? Discuss (http://forum.thefreedictionary.com/postst93239_Incident-at-Xuanwu-Gate--626-CE-.aspx)