Let me give you advice before you told him you are not the father you need to make two or three DNA test to make sure because it always happen mistakes on the test do not stress yourself just make more test hair follicles and cheek swab so then you will be sure . After if they said it is not your Son after that you need to talk with the mother if she wants to tell the truth good if not you are not the Biological father you are the adoptive father you raised him he is your son forever do not worry about the DNA result just look for a good lawyer with good review so you will get so many ways to start process to ur son. Be strong keep praying God will help you and your son .