And according to Pretty Little Liars' Brendan Robinson, there has been a certain hint all along that everyone has probz missed.
"I won’t tell you what specific clues there are but there are hints that have been dropped for a long time,” he told ET, adding that he was “thrown off” when he discovered who it is.
“When I found out who it was, I hadn’t read the script yet, because it was a couple weeks in advance and it didn’t make total sense to me at first,” he explained.
“And then, when I saw the script and I read it and we all sat down - and the people that are involved in those scenes do a really, really phenomenal job - all the questions are answered and it made sense.”
Robinson, who plays Lucas Gottesman, also revealed that the finale will include flashbacks to show peeps the A.D. clues that they missed.
"Yes, there are a lot of flashbacks in the finale,” he said. “You will see those things, and several of the things are not spoken but you actually see it as [a way to remember].”
Which begs the question, is Robinson's character, Lucas A.D.?
“It’s possible,” he coyly responded.
“I hope that after seeing that last scene that people cut Lucas some slack,” he continued. “So, maybe if he is involved in the whole thing they realize there is a motive behind it,” he added.
“I’ll say this, if he is involved, I think it's for a good reason,” he said. “He is trying to protect Hanna for a good reason.”
Check out the whole interview below!