 In 1035 Isma'il's brother Harun was assassinated by his guards at the instigation of the Ghaznavid sultan Mas'ud I of Ghazni.Isma'il took control of Khwarazm, and like his brother defied Mas'ud and gave support to the Seljuks, who were also hostile to Mas'ud.In response Mas'ud turned to the Oghuz Yabghu (chieftain), Shah Malik, for support, inviting him to take over the governorship of Khwarazm.