Why does he not care?

So before I met my husband he had a kid. He was 7 at the time now he's 14. Whenever I bring him up he always dismisses it I don't get y is he ashamed of him. I also believe his dead beat way he is embarresd about so he makes me look like I'm the jealous type that would never accept his kid which is not the case. I just find it so weird because he hasn't seen his kid since 2010. He lives in dominican republic, the other weird part is the kid doesn't have his last name. Why would he make me look like the bad person that's so wrong. I wanna find out my self out of what's going on because if he's making me look bad I wanna set the record straight. His sister in law doesn't like him much so I was planning when we go to the lake she will give me answer I'm searching for. What's sad about this is we have a kid together and he is great to him puts his pictures all over Facebook, but he never mentions his other son. I'm so confused and don't know what to do. It's his bussiness because it's not my kid but y not be proud of him and acknowledge his existence, instead of denying him. Please help