What to do if you found out that your fiance has a child from the past?

Heres the thing, when we we're still dating, He gave me all the password of his friendster and facebook 2 years ago, I did not care to check it for I did not gave mine, I still believe I need privacy. until one time I checked his friendster, which is not already active for a long time, I found out a message on his trash items, a girl messaged him informing about a birthday of her child. I was so shocked I never heard even rumors he had a child. He confessed to me that he is not sure, he is the father, it was a product of one night stand, he was 1st yr of college and moved to another city, he met the girl as a singer in a club, the had sex and after that there was no communication from the girl. My fiance was a star basketball player in his school and he said he practice to the gym everyday but the girl never bothered to go directly to him or even the girls family who lived near the school did not bother him at all. He have not seen the child, so he thinks the girl is just making up stories. As we are about to plan for our wedding I was so curious last night to search for thr girl in Facebook and I found pictures of the child, who I think looks a lot like him, it tore my heart. I have mixed emotions, they did not communicate with him, I told him last night that the child who is 8 yrs old now, looks a lot like you. and He said if he is really mine I will accept her wholeheartedly, I admire him for that. But I was so shocked about this thats happening I dont know how to explain to my family who really loved my fiance. I loved him and help me what will I do to get through this before we get married.