Li Yuanji
By this point, Li Shimin and his older brother Li Jiancheng, who was created crown prince in 618, reportedly after Emperor Gaozu first offered the position to Li Shimin due to his contributions, were locked in an intense rivalry, as Li Shimin's accomplishments caused people to speculate that he would displace Li Jiancheng as crown prince, and Li Jiancheng, while an accomplished general himself, was overshadowed by his younger brother. The court became divided into a faction favoring the Crown Prince and a faction favoring the Prince of Qin. The rivalry was particularly causing problems within the capital, as the commands of the Crown Prince, the Prince of Qin, and the Prince of Qi (i.e., Li Yuanji) were said to have the same force as the emperor's edicts, and the officials had to carry conflicting orders out by acting on the ones that arrived first. Li Shimin's staff was full of talented men, but Li Jiancheng was supported by Li Yuanji, as well as Emperor Gaozu's concubines, who had better relationships with Li Jiancheng and Li Yuanji than they did with Li Shimin.