How did Antiochus IV Epiphanes come to power as Seleucid king?

Antiochus IV Epiphanes ascended to the Seleucid throne in 175 BCE following a period of political instability. His brother, King Seleucus IV Philopator, had been assassinated by his chief minister, a usurper named Heliodorus.12

At the time of this assassination, Antiochus had recently returned from Rome, where he had spent many years as a hostage following his father’s defeat by the Romans. Upon his return, he successfully ousted the usurper Heliodorus to seize power for himself. His claim to the throne was further solidified by the fact that the rightful heir, Demetrius (the son of Seleucus IV), was being held as a hostage in Rome at the time.21