King Guy was released from prison by Saladin in 1189. He 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. However, it was still not enough to counter Saladin's force, which 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.