Half sibling

Okay so me and my ex/baby dad are not on good terms, like he doesn't see our son, hasn't in months, we don't even speak now. He has a new son that's over a week old now with his new girlfriend, and honestly at first I could've cared less about him being around my son or ever meeting him but now it kind of bothers me. I know that my ex will never bring that kid around our son and his girlfriend hates me, but I feel like he should be able to be around his half sibling, whether we like to admit it or not they ARE brothers and I don't want it to be kept from him until he just randomly finds out one day that he has a brother ya know? He's only 2 but I mean I don't want to keep the fact that he has a brother from him buuuut I also don't want to have to explain to him that he has a brother he can't even see.. It's a complicated situation. Even though we all have our issues I would love for my son to grow up with his little brother, I know that will never happen sadly, because they choose to be petty over dumb things..