How does a father feel when he finds out the child he has raised is biologically not his?

A real father would not feel any differently. He has raised the child and so that child is his, it's the way it works. It's not all biology, it's about responsibility of a father to this children and family. How would the child feel if after 8 years their father suddenly declined to raise or care for them anymore? A true man would look past that and do what is right. The woman on the other hand has neglected her responsibility to her partner. Honesty. There might be some problems in that department.