Harry Potter was actually the son of Lord Voldemort to an unknown mother and was made to grow up as the 'boy who lived' so that the Riddle bloodline could continue on secretly. Harry knew all about it from Sirius when he helped him escape from Azkaban and had been forced to act like he was against his own father in order to protect him. Harry was lying to everyone on Hogwarts about his encounters with Lord Voldemort. They never happened. 

Harry Potter is Tom Marvolo Riddle, Jr.