He was the son of the Herodian prince, later king Tigranes VI of Armenia and his wife Opgalli.
In the spring of 58, his father was crowned as king of Armenia by Roman Emperor Nero in Rome and ruled until 63.
Alexander had a sister called Julia, who married the Anatolian Roman Senator Marcus Plancius Varus.
After the betrothal, Nero crowned Alexander and Iotapa as Roman client rulers of the small Cilician region of Cetis, which had previously been ruled by Alexander's Seleucid ancestors, then by Archelaus of Cappadocia, and then by Archelaus of Cilicia and Antiochus IV.
[1] There are three princes by the name Phasael in the Herodian dynasty, all three mentioned by Josephus in "War" (BJ) and "Antiquities" (AJ):[2]