 Some years earlier, Roger II's daughter, Constance of Sicily (William II's aunt) had been married off to Henry who was son of Emperor Frederick I and would later become Emperor Henry VI, meaning that the crown now legitimately transferred to him.Such an eventuality was unacceptable to the local barons, and they voted in Tancred of Sicily, an illegitimate grandson of Roger II.During his reign Tancred was able to put down rebellions, defeat an invasion by Henry VI and capture Empress Constance, but Pope Celestine III forced him to release her.