The Final Horcrux

"What if, during the Battle of Hogwarts, in Harry Potter's final duel with Lord Voldemort, having discovered and destroyed all seven Horcruxes (including the unintentional one contained within himself), ready to face down his enemy, now a mere man as mortal as any other, something went wrong? What if there was another, secret Horcrux?" Voldemort!Wins AU