In 210 BC, his father made him joint king, when Antiochus III went off to the East on his great expedition.
[2] He is not recorded to have had any real independent authority, but he was appointed viceroy of the eastern Seleucid satrapies.
[4] In that year, his father arranged for him to marry his younger sister Laodice IV.
[2] From their sibling union, Laodice IV bore Antiochus a daughter called Nysa.
[5] In 193 BC, Antiochus III appointed his daughter, the sister-wife of his son, Antiochus, as the chief priestess of the state cult dedicated to their late mother Laodice III in Media.