Li Yuanji [SEP] sister
Liu Heita returned from Eastern Tujue and reoccupied old Xia territory, Li Jiancheng, at the suggestion of his staff members Wang Gui and Wei Zheng, volunteered to lead the army against Liu. Emperor Gaozu thus sent Li Jiancheng, assisted by Li Yuanji, against Liu. Around the new year 623, with Liu's forced bogged down while attacking Tang's Wei Prefecture (魏州, in modern Handan, Hebei), Li Jiancheng and Li Yuanji engaged him at Guantao (館陶, in modern Handan as well), crushing him
the oldest son of Li Yuan the Duke of Tang, a hereditary noble, and Li Yuan's wife Duchess Dou, who was herself the daughter of Dou Yi (竇毅) the Duke of Shenwu and Northern Zhou's Princess Xiangyang. Duchess Dou would subsequently give birth to three of Li Jiancheng's younger brothers -- Li Shimin, Li Xuanba (李玄霸, who died in 614), and Li Yuanji. She also gave birth to a sister of Li Jiancheng's, the eventual Princess Pingyang, although it was not clear