Father or Baby Daddy?

A year ago I found out the man that raised me and who name is on my birth
certificate isn't my biological father. I am now thirty-six years old and is now
a father myself. The man that raised me and my mother is still married and
living a confortable life in a small town in  Arizona. I grew up believing that
he was my natural father. I was surprised when I was by my Uncle John that he 
believe he was my biological father. He suggested we take a paternity test,
which we did. It came back 99.9999% that he was my biological father. He has
colon cancer and only have a  few months to live. His wish is to be an active
part of me and my family's life. I haven't said anything to my parents. A a part
of me wants to confront my mother. How could she go all of these years having me
think that  her husband was my father? On the otherhand, he has been the best
father a child could have. I don't want to break his heart this late
in life. Should I reject my biological father and live life out as planned by my
mother. Or should I confront my mother? 
From: Mama's baby, Daddy's maybe.