I don't know what to think

Edit: Apparently they reached out to him when she was 14. He agreed to do paternity testing several times but they never would meet up. He said every once in a while the girl reaches out and asks how he is doing. But then doesnt say anything else. He had full custody of his son from his previous marriage and was a wonderful dad. The son passed away from a rare brain disorder, about a year before they first reached out. He has also raised my daughter as his own and we finish off the adoption next month. He said if he would have known earlier on he would have went to court to get rights. He said he only hooked up with the mom once ( which I know once is enough) after i posted this i had a message from the girl asking for my husbands number because they were trying to do something. Husband never denied anything and when I asked him who she was he told me the whole story. He said he was sorry for getting mad earlier he just felt overwhelmed. I just feel like my whole family has changed. I am fine with him pursuing a relationship if she is his, but I don't think that is what he wants to do at this point.

So today my husband and I were sitting on the couch and i get a friend request from a girl. She was a mutual friend with my husband. I asked him who she was. He precedes to tell me that he hooked up with her mom when he was in college and the mom is claiming that this is his daughter. The girl is probably 17 and has a child as well. My husband doesn't think she is his, and he said they never reached out until a few years ago. I don't have a problem with him having a child, i didnt know him then, but this is just alot thrown at me. I asked him why hes never told me any of this. Now he's mad at me. I feel like I have a right to be a little upset. I just don't know what to think.