Ptolemy XIII, 61?–47 BC, king of ancient Egypt (51–47 BC), of the Macedonian dynasty; son of Ptolemy XII. On the death of his father he was under the guardianship of Pompey. He was completely overshadowed from the start by his brilliant and celebrated sister, Cleopatra, who became his wife and ruled with him. She disagreed with his advisers, notably the eunuch Pothinus, and fled to Syria. She came back (48 BC) with an invading army. At this juncture the defeated Pompey arrived seeking refuge and was put to death by Pothinus. Julius Caesar followed immediately. He fell under the influence of Cleopatra, forced Ptolemy XIII to share the throne with her again, and put down a rebellion raised by Pothinus. Ptolemy was thus defeated. He drowned accidentally in the Nile.