Answer
Cleopatra Thea, the daughter of Seleucus IV Philopator, became the ruler of a Syrian pocket against Alexander II Balas in 128 BC. Her brother, Demetrius II Nicator, was exiled to Crete due to his father's death. Seeking to regain the Syrian throne, Cleopatra Thea married Alexander II Balas, who was backed by the Romans, and gave birth to Antiochus VI Dionysus.