After weeks and weeks of fan speculation, Pretty Little Liars dropped a major bomb in its last episode: Spencer's twin was confirmed on the Pretty Little Liars finale. It turned out Mary Drake did have one more secret child after all, which was a theory that had been gathering steam throughout the seventh season. Every time it seemed like Spencer was acting out of character, it felt like even more evidence that she was really someone else. And now it has been confirmed that Spencer did have another sister, a British former bartender named Alex Drake.
Spencer discovered Alex after being kidnapped by Mona and dropped in a strange cell in an unknown (at first) location. When Spencer drowsily woke up, she thought she was looking at her own reflection in the glass walls until Alex gave her a fright. What unfolded over the rest of the episode was a stunningly twisty and totally bananas tale that introduced viewers to Alex Drake, who had been pretending to be Spencer for well over a year. Alex explained her origin story and how she became involved in Rosewood, filling in all the gaps of the last season even if she didn't answer all the questions right away.
Mary Drake provided the rest of the exposition. She had never revealed to the Hastings that she was pregnant with twins, instead cutting a deal with the doctor to give one of the girls to a wealthy family in England for a monetary payout. She assumed Alex would be living in the lap of luxury, but that wasn't the case. Alex's psychological issues led her adoptive family to abandon her at an orphanage, where she grew up feeling unloved and unwanted. Then a coincidence brought her closer to Rosewood.
While working at a bar in London, Alex ran into Wren totally by accident. He assumed she was Spencer, but quickly realized what was really going on – the accent and eyeliner were probably the biggest tip-offs. He revealed her familial origins to her and eventually introduced her to her sister Charlotte, setting Alex on the path that led her back to Spencer. She rewarded Wren for that by murdering him and turning him into a diamond necklace, so he was always near her heart. Alex was hardcore.
One by one, all of the scenes where Spencer had acted out of character were revealed to have been Alex the whole time: Hanna's "vision" while kidnapped; Toby and "Spencer" hooking up after Yvonne's death. Fans had figured it out long before the show confirmed it, but it was still deeply satisfying to see each reveal play out on screen.
Spencer having an evil twin may have felt like the craziest theory out there at first, but it made the Pretty Little Liars finale an impossible one to forget.