Guy of Lusignan, who had been refused entry to Tyre by Conrad, began to besiege Acre in 1189. During the lengthy siege, which lasted until 1191, Patriarch Heraclius, Queen Sibylla and her daughters, and many others died of disease. With the death of Sibylla in 1190, Guy now had no legal claim to the kingship, and the succession passed to Sibylla's half-sister Isabella. Isabella's mother Maria and the Ibelins (now closely allied to Conrad) argued that Isabella and Humphrey's marriage was illegal, as she had been underage at the time; underlying this was the fact that Humphrey had betrayed his wife's cause in 1186. The marriage was annulled amid some controversy. Conrad, who was now the nearest kinsman to Baldwin V in the male line, and had already proved himself a capable military leader, then married Isabella, but Guy refused to concede the crown.