Saladin released King Guy from prison in 1189. Guy attempted to take command of the Christian forces at Tyre, but Conrad of Montferrat held power there after his successful defence of the city from Muslim attacks. Guy turned his attention to the wealthy port of Acre. He amassed an army to besiege the city and received aid from Philip's newly arrived French army. The combined armies were not enough to counter Saladin, however, whose forces besieged the besiegers. In summer 1190, in one of the numerous outbreaks of disease in the camp, Queen Sibylla and her young daughters died. Guy, although only king by right of marriage, endeavoured to retain his crown, although the rightful heir was Sibylla's half-sister Isabella. After a hastily arranged divorce from Humphrey IV of Toron, Isabella was married to Conrad of Montferrat, who claimed the kingship in her name.