The final episode of "Pretty Little Liars" finally aired and the fans are experiencing some sort of a bittersweet mix of emotions as they find out who A.D really is. Before proceeding to read the rest of the article, be warned that it contains major finale spoilers. To continue, it turns out that the twin theory was real. Just like in Sara Shepard's book series, which the TV show was adapted from, there was a shocking twin theory in the final episode. However, the characters that had a twin in the finale episode were not the same in Sara Shepard's book.
There was a slight tweak in the series version, as it turned out that Spencer was the one who had a twin.
The haunting initials of A.D. no longer led to Alison DiLaurentis, but instead, it actually meant Alex Drake. In previous episodes, it was revealed that Mary and Jessica were twins, and the fans thought that the twin theory only stopped there. However, the "Pretty Little Liars" finale revealed that after Mary Drake gave birth to Spencer, she also gave birth to a second child whom she named Alex.
Alex and her exile in England
Right after she was born, Mary Drake put Alex up for adoption, and a family from England took her in. The Hastings never knew about Alex's existence.
However, a few years after adoption, the family from England noticed some issues with Alex's behavior, and they decided to put her into an orphanage and changed her last name back to Drake.
The fact that Spencer has a twin can now explain that it wasn't her who met Wren at the airport in the previous episodes.
Looking back, Wren actually played a very crucial role in the story, because without him, Alex would've never known about Spencer. Theories that Wren was part of A's army was actually true since he was affiliated with Alex, who turned out to be Uber A.
Vengeance for Charlotte
When Charlotte died, it was the time when Alex decided to return to Rosewood to get vengeance for her half-sister. "Pretty Little Liars" Season 7 finale also gave the viewers comprehensive flashbacks to make them understand the relationship of Alex and Charlotte. Apparently, the two became close friends when they grew up, which explains the anger that Alex felt when she knew about Charlotte's cause of death.
Fans who have read Sarah Shepard's "PLL" ending can somewhat see a similarity between Alex and Courtney - the evil twin in the book series. Aside from her desire to avenge Charlotte's death, Alex targeted the liars because she felt so jealous that they pretty much had everything she didn't - family, friends, and even a chance to be treated in a proper psychiatric facility.
