Humphrey had defected from his cause and caused the destruction of the baronial rebellion in 1186. He would not have been able to get suport as king of Jerusalum so those in power made his marriage to the heir of Jerusalum void.
Marriage to Humphrey of Tibnine was annuled so that she could be wed to Conrad of Montferrat, who was well-connected and had proved his ability and strength of his personality.