Meanwhile, friction had been developing between Li Fuwei and Fu Gongshi. It had been that for years, the army, knowing the great friendship between Li Fuwei and Fu, honored Li Fuwei as its father and Fu as its "uncle." Eventually, however, Li Fuwei became suspicious of the respect the army had for Fu, and began to give more authorities to Wang Xiongdan and Kan Leng, giving them effective command of the army. When Fu realized that Li Fuwei was suspecting him, he became resentful, but pretended to lose interest in the army, instead studying
alchemy with his friend Zuo Youxian (). In 622, Li Fuwei, fearful that Emperor Gaozu might doubt his loyalty, went to the Tang capital
Chang'an to pay homage to Emperor Gaozu, taking Kan with him. Before he departed, he left Fu in command, with Wang as Fu's deputy, in actual command of the forces, secretly warning Wang, "If I suffer no ill consequences, make sure that Fu does nothing rash." When Li Fuwei got to Chang'an, Emperor Gaozu gave him the special treatment of allowing him to sit with Emperor Gaozu on the imperial seat and, at other occasions, honor even above Emperor Gaozu's son
Li Yuanji the Prince of Qi. However, he did not permit Li Fuwei or Kan to return to Danyang, making Kan a general. Once Li Fuwei left Danyang, Zuo persuaded Fu into planning a rebellion. However, Wang had actual command of the army, and therefore, Fu decided to trick Wang by claiming that Li Fuwei was doubting Wang's loyalty. Wang, angry over the revelation, gave up command of the army, and Fu took control and then tried to persuade Wang to join his plot. Wang, realizing that he had been tricked, nevertheless refused to join Fu, so Fu strangled him. In fall 623, Fu, claiming that Li Fuwei had been detained by Emperor Gaozu and had ordered him to rebel, did so. He soon declared himself the Emperor of Song, and he was able to get another rebel leader who had submitted to Tang as well, Zhang Shan'an (), who controlled the modern northern
Jiangxi and eastern
Hubei region, to submit to him. Emperor Gaozu sent his generals
Li Xiaogong the Prince of Zhao Commandery (the son of his cousin),
Li Jing, Huang Junhan (), and
Li Shiji against Fu, with Li Xiaogong in overall command. In winter 623, Zhang was captured by the Tang general
Li Daliang, cutting off a flank support for Fu. == Defeat and death ==