He was son of king Antiochus X Eusebes and the Ptolemaic princess Cleopatra Selene of Syria, who acted as regent for Antiochus XIII after his father's death sometime between 92 and 85 BC. Some time after Tigranes had conquered Syria (83 BC), she traveled to Rome to have her sons recognized as kings of Egypt, but to no avail. However, between 75 BC and 73 BC, they were recognized as "Kings of Syria", and "maintained a royal state". Selene was eventually captured and killed by Tigranes. However, after the latter's defeat by Lucius Licinius Lucullus at the Battle of Tigranocerta, the residents of Antioch hailed Antiochus XIII as king, and Lucullus approved his appointment as client ruler of Syria (69 BC).