my first husband just had a child!

My first husband accused me of cheating on him during our first year of marriage. I didn't!!!! We separated last year because of this and this was barely 4 months after our wedding.     We have started the divorce process... today, I received a message from my cousin that my first husband had a baby who is now 3 months. From my calculations, it means that he got the woman pregnant when we were married but was constantly accusing me on being the unfaithful one... 
I am not angry, not at all. Instead I am happy to be free. I sent a message to him on Facebook to congratulate him on the birth of his child. Maybe it sounds petty to have done that but I just want him to know that I know! 
Update: he replied back lol see the picture attached! What a joke!