The Vampire Diaries Joseph Morgan spoiled that tonight's episode, "The Five", is one of his favorite episodes this season. Morgan also reveals that we will learn a huge secret that fits into the mythology of Mystic Falls and the Originals' history.
"It's really a big reveal and will play a dominant part in how the season evolves." Executive producer Julie Plec also tells us, "The question of what is different about [Connor], why is he able to deeply, darkly hunt and kill vampires, what drives him, what his history is and what other people know about his history start to unfold ... in that flashback."
Source: TV Guide