 When Shibi Khan besieged them there on September 11, Empress Xiao's brother Xiao Yu suggested seeking further assistance from Princess Yicheng, who—pursuant to Turkish custom—was entrusted with overseeing military affairs at home in her husband's absence.She sent the khan a false report of a northern attack on the khaganate; between this and reports of numerous Chinese reinforcements rushing to answer the emperor's call for help and extravagant promises of reward and promotion, the khan decided to lift the siege and return north.