Riddle me this...

Something I came across in my current read. See if you can answer this:

Bobby and his father are in a horrible car accident, which instantly kills Bobby's father. Bobby is seriously injured and rushed to the hospital. The surgeon takes one look at Bobby on the operating table and says: "Oh my God! I can't operate on this boy... he's my son!"

How can this be?

What you think?

xoxo