Is it weird that he has kept an ex a completely secret

My boyfriend and I have been together for 3 and a half months. He has this ex that he does not talk about. Idek her name because he and his best friend referred to her as she-who-must-be-named. The only reason I know about her is because SOMETIMES she gets brought up by his best friend. For example one of my friends decided to remain friends with someone who abused me badly and my boyfriend said he feels a true friend isn't gonna be friends with someone who abused you and isn't afraid to stick up for you. His best friend said "I agree. Just look at my Facebook and Twitter history for the last 7 years between me and she-who-must-not-be-named. Another time I was telling them about Colleen Ballinger and her being in group chats with minors and showed his best friend her ukulele "apology" and he jokily says "She-who-must-not-be-named is that you?" I don't know anything about she-who-must-not-be-named and I did ask once and he says "She's my ex who we don't talk about." I get he has a past before me and he doesn't have to tell me everything but if he won't even say her name then clearly this is a BIG ex. Shouldn't I know about that?