Frederick had been King of Jerusalem—and as such claimed suzerainty over Cyprus—in right of his wife Isabella II until her death in 1228. That year he arrived first in Cyprus, where he antagonised the nobles, and then in Jerusalem, where he stayed until 1229, leaving in humiliating circumstances after having produced an anti-imperialist reaction in the people. In 1231 he sent Riccardo Filangieri as his marshal. His attempt to assert his authority was opposed by John of Ibelin, the Old Lord of Beirut, who had been regent until Frederick's arrival. On John's death in 1236 the war was taken up by his son Balian. In 1239 Philip of Montfort assumed the leadership of the opposition. Though the ecclesiastical hierarchy and the Knights Templar supported the nobility, the Teutonic Knights and Knights Hospitaller supported Filangieri. In general his rights as regent were recognised but his practical power was denied on the basis of the Assizes and the Haute Cour. His headquarters were in Tyre and he had the allegiance of Bohemond V, Prince of Antioch and Count of Tripoli. He also held the Holy City of Jerusalem itself, which had been negotiated away from the Saracens by Frederick. So long as the Ibelins controlled the opposition, Filangieri could count on the support of their enemies as well. The Italian cities were also divided between the two factions: Pisa supported Filangieri and Genoa the Ibelins. The Ibelins controlled Beirut, Arsuf, and Caesarea as well as the old capital of Acre. In 1231 the citizens of Acre formed a commune with their headquarters at the church of Saint Andrew's in order to unify their opposition to Filangieri. In 1232 John of Ibelin was elected its mayor.
Question: Who was Balian's father?
Answer: John of Ibelin