My question involves paternity law for the State of: PA

Years ago, while my husband and I were going through some tough times, I had an affair that resulted in pregnancy. I did not know if my husband or the other guy was the father, the other guy knew I was pregnant. The baby was born and since we were (still are) married, my husbands name was put on the birth certificate. When he was 6 months old, we found out my husband is not the biological father. The other guy did not have a test done, but admitted he was the father. My husband didn't care then, and still doesn't care that he isn't the biological father, he views him as his son and has supported him in every way. The biological father walked away when the child was 9 months old, but popped up every year or two. He hasn't seen the child since he walked away, and the child is now 6 years old. The biological father now wants to be recognized as his father, and wants my husbands name off the birth certificate. My husband has been there when I was pregnant with him, and everyday since he was born. Can the biological father come back after years and get parental rights? By the way, my husband and I were married 6 years when this happened. We are now married for 10+ years.