It's been a long time coming, but, on Tuesday night, fans finally discovered who A.D. is on Pretty Little Liars. It was just as shocking and delightfully twisted as we've come to expect from the show, but the reveal that Alex Drake, Spencer's secret twin sister, is A.D. was also really confusing. Though the Pretty Little Liars finale did manage to explain some of the hows and whys regarding it all, there were still gaps left open there. And there's definitely at least one thing you need to understand about the A.D. reveal on PLL that you possibly didn't get during the episode.
Specifically, you may have been wondering how long showrunner I. Marlene King been plotting this reveal and how Alex Drake fits into the PLL timeline overall. Thankfully, in an insightful interview with the New York Times, King revealed, as many fans suspected, that twins were an important part of Pretty Little Liars from the beginning. She explained that, "We started playing with the twin theory early on. We didn’t know who the twins were going to be, until about Season 3. It runs in the family. They say it skips a generation, but they just got lucky."
However, King also divulged that part of this due to remaining loyal to Sara Shepard's original book series upon which the show is based:
Which, if you've been re-watching the early seasons of the show in preparation for the finale (or have a tremendous memory), will make total sense to you as a fan. The recurring theme of twins in PLL has been evident since Season 1 of the show, with the motif showing up in dream sequences or in creepy background details, such as photos or symbolic mirror imagery.
However, fans looking to find evidence of Alex's existence in PLL's earlier seasons might be disappointed to discover that they won't find any deliberate proof there.
As King explained in the same interview, the decision for Spencer's secret twin to be A.D. was made after Season 5. Though there might not be visible evidence of Alex throughout the entirety of PLL, the character and her motives still certainly fit the timeline, as King revealed:
This revelation may be a little disappointing for those of us wanting to re-watch every PLL episode from the beginning in order to scoop up clues about this reveal. However, there's still something deeply satisfying about PLL remaining true to the original themes of twins and using that theme to deliver a conclusion that we should have seen coming.