The family was irreparably split apart when Philip took a girl younger than Alexander for his new wife. This girl, pregnant with a child by Philip, divided the royal house into two bitterly hostile camps because of her family connections. When the satrap of Caria in the Persian Empire, was trying to marry his daughter to Philip's retarded son, Arridaeus, Alexander feared that Philip intended to make Arridaeus—Alexander's half-brother—his successor. Philip learned of the plot before it was carried out, however, and placed Alexander under house arrest. Always the ultimate politician, he placated Olympias's brother, by offering him his daughter's hand in marriage, despite the fact that Cleopatra was the king's niece. After his father's murder in 336 bc Alexander became King Alexander III. Given the suspicious nature of Philip's death, however, Alexander found himself surrounded by enemies at home and threatened by rebellion abroad.