李泰
Later in 643, when Li Chengqian, fearing that Emperor Taizong would depose him in favor of his more favored brother Li Tai the Prince of Wei, was revealed to have plotted with Hou Junji to overthrow Emperor Taizong, Emperor Taizong had Zhangsun, Fang, Xiao Yu, Li Shiji, along with the responsible officials at the legislative and examination bureaus and the supreme court, investigate the matter. They confirmed Li Chengqian's guilt, and Li Chengqian was subsequently deposed, although Emperor Taizong, believing that Li Tai's machinations were responsible for Li Chengqian's downfall, exiled Li Tai as well and created another son, Li Zhi, crown prince. He subsequently made Zhangsun, Fang, and Xiao Li Zhi's senior advisors.