Just supposing you had say a one night stand with a woman. She later came back to you and said she was expecting a baby and it was yours. Even through your relationship was over you decided to be a father and involved in the childs life.

Later on some things happen, you do a DNA test and discover you are not the father.

Would you still be a father? Would you still do what you can to help raise the child even though biologically it isn't yours. Hell even legally at that point its not yours.