That's not the clue, though, this is: "The weekend you said she disappeared," he tells Aria in a serious voice, "I saw her that weekend." Say what? How is that possible? What does it mean? This seems like it could be a huge clue about what happened.
Here are our top guesses about what this revelation could lead to:
Duncan saw Alison before she died, and she told him something important: The clip cuts off after Duncan's statement, so it's possible he's not implying he saw her after she supposedly disappeared. Maybe he's going to go on to say, "I saw her earlier, and she told me [insert huge clue here]."
Alison is alive: On the other hand, maybe it does mean that Ali isn't as dead after all. How? We don't know, though, as we've said before, with Rosewood's incompetent and corrupt police department, we wouldn't put it past someone to fake the records on the body that's supposed to be Ali's.
Alison was alive after disappearing, and killed later: The Little Liars seem to assume Ali died the night she disappeared, but what if her death happened well after her disappearance? Maybe she ran away, only to run fowl of someone.
Alison has a twin: It happened in the books, and it could happen in the show. Maybe it's Alison's twin that Duncan thought he saw or talked to that weekend. Alternatively, maybe it's Ali's twin who is dead, and Ali is alive and well, somewhere.
What do you think this sneak peek means?
Be sure to tune in for the next episode of Pretty Little Liars tonight on Monday, March 5 at 8 p.m. ET/PT on ABC Family.
Pretty Little Liars airs Mondays at 8 p.m. ET/PT on ABC Family.