“Ananus...called together the Sanhedrin and brought the brother of Jesus the so-called Messiah/Christ, James by name, together with some others. He accused them of breaking the Law and condemned them to death by stoning. But the experts of the Law who were more liberal were angry at this and secretly requested the king stop this from happening” (Jewish Antiquities, Book 20).

Paul is believed to be telling us in Galatians 1 that nobody could have given him the gospel for instead of going to the apostles in Jerusalem he went to Arabia.  The idea is that Jesus' appeared to him and was teaching him.  He went to Jerusalem in the end.  His doctrine that if he himself or the apostles change the gospel then ignore them which is a way of stressing that it is all from Jesus.

Calling James the brother of the Christ or the Lord was a title given to James by the early Church. In Galatians 1:19, Paul says that he met James the Lord's brother. This seems to say that Jesus lived in the first century when his brother was still alive. But the most important thing to realise is that Paul told Philemon that Onesimus the slave was to be his blood-brother and not just a brother in the Lord so blood-brother among the early Christians didn’t always mean that you shared a parent. According to the letter of Paul to Philemon Christians believed you could make somebody you loved your brother or sister by blood even if they were not a blood relation. Paul told Philemon that Onesimus was not just a brother in the Lord but a blood brother from now on. A brother in the Lord means a non-literal brother but Paul’s saying Onesimus who was not related to Philemon was more than that and a blood brother indicates plainly that you can become a literal blood brother by adoption. This practice could have confused people about James and made them think he really was born a brother of Jesus’. Josephus who also called James Jesus’ brother could have made a mistake due to this confusing practice. The practice probably had a lot to do with the universal accusations of incest against Christians that supposedly were rife among the pagans.

In James 5:10, James offers the prophets as role models and singles out Job for mention. The real brother of Jesus would have stressed Jesus as role model. Why would Jesus' brother mention the suffering of prophets inferior to Jesus and not Jesus'? He never calls Jesus the Son of God or hints that Jesus lived a perfect life before his glorification. It seems that James did not even think that Jesus was the best exemplar. He had very little interest in Jesus in his epistle. This suggests that James was not his brother at all and knew very little about him.

Maybe Josephus was saying James brother of the so-called Christ as in a sneer. That would mean the line can’t prove if Jesus was thought to have existed or not. Also what if Josephus was calling James under a Jewish nickname “Brother of the So-called Christ”, called to him in mockery for following a false or non-existent Christ.

Josephus would not call Jesus the so-called Christ when it was not the Jews or the Romans were calling him Christ but a tiny persecuted and obscure sect. 

We must face the possibility that somebody altered Josephus's text to make it deceitfully call James the brother of the so-called Christ, Jesus. This was somebody who didn’t like the fact that Jesus was ignored by Josephus but who knew that Josephus couldn’t be positive about Jesus and would speak of him as a so-called Christ.