text: That question is not as straight-forward as you might imagine. Some states (like California where I practice) have "presumed father' and "putative father" statutes. Basically, any child born of a marriage is PRESUMED to be that of the husband. You can defeat that presumption in a number of ways. HOWEVER, the time limit for rebutting that presumption is short. In California, I believe it's two years. After that time, the presumed father becomes the legal father forever. After that two years has passed, you could have proof positive that you're not the father and it wouldn't do a d#mn bit of good.