"No. I was given a transfusion of blood that was heavily mutated by gamma radiation. That transfusion activated a rare gene - a gene that I possess, along with a select few others - which in turn caused me to gain some strength, stamina, healing ability, muscle mass, and to turn green when I feel in the mood. You could drop the Empire State Building on me and I'd walk away whistling."

This might be the understatement of the last millennium. Or two.