Let 'You' be Y, and 'my father' be X.
Step 1: X marries the unrelated female Z, with issue B, who subsequently marries Y's daughter. (Y is B's father in law). Z dies.
Step 2: X marries Y's sister, with issue Snoggs. (Y is X's brother-in-law and X is Snogg's father.)
Step 3: X and Y each have one surviving parent; these parents marry; X and Y are hence step-brothers.
Posted by broll
on 2011-09-26 21:42:08