“Now we will tell what took place under Antiochus Eupator, who was the son of that ungodly man. We will give a brief summary of the principal calamities of the wars. This man, when he succeeded to the kingdom, appointed one Lysias to have charge of the government and to be the chief governor of Coele-syria and Phoenicia.”
This biblical author clearly states that he is going to talk about King Antiochus V, Eupator. He used the first person plural “we” here. He really disliked King Antiochus IV, his father Epiphanes, whom he called ungodly, even after his deathbed conversion. He did not mention that the new king was only 9 years old. King Antiochus V ruled for only 2 years until he was 11, when he was killed. He had been brought up by Lysias who gave him the name of Eupator, so the fact that Lysias was in charge did not seem that unusual. In fact, Philip was aware of this situation and had fled to Egypt.