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The Vampire Diaries" returns Thursday night with a flashback episode "1912," and it's going to be quite a game changer.The episode will not only explain the centuries-long rift between Stefan and Damon, the Salvatore brothers, but it will also reveal the season's biggest mystery: Who's Mystic Falls' creepy serial killer? "We discover the identity, and it's a pretty shocking moment," Paul Wesley, who plays Stefan, told HuffPost TV in a ...