Seleucus II Callinicus
After Antiochus II died his second wife Berenice declared her son Antiochus king at Antioch while his first wife Laodice declared her son Seleucus king in Ephesus. Since Antiochus was too young to be able to rule, Seleucus and Laodice had Berenice killed so that Seleucus no longer had any challenger for his throne. Ptolemy III Euergetes was angry about this so he invaded Syria and started a war.