Pretty Little Liars revealed one of the series' biggest lingering questions on Tuesday night: Who killed Charlotte (Vanessa Ray)?

It turns out that Mona (Janel Parrish) was the one who pushed Charlotte out of the bell tower the night that Charlotte was released from the mental hospital. Mona saw through Charlotte's alleged redemption and knew that the former A was itching to get back to torturing people again. Mona wasn't about to be another pawn in the game, so she confronted her nemesis. The two got into a fight and Mona pushed Charlotte into the steel pipe that killed her by accident. Mona threw the body out of the bell tower and has been hiding from A.D. ever since.

Vanessa Ray, <em>Pretty Little Liars</em>Vanessa Ray, Pretty Little Liars

The reveal of Charlotte's murderer relieved at least some stress for the Liars. It was the main question A.D. wanted to answer, and as a reward, the cyber stalker took Archer Dunhill's (Huw Collins) body out of Aria's (Lucy Hale) trunk and buried it in Charles DiLaurentis' false grave. The girls were almost busted by the police over the burial spot, but Mary Drake (Andrea Parker) came through and confessed — removing all of A.D.'s blackmail leverage.

Going into the series finale next week, the girls are allegedly free from A.D. In fact, their tormentor was last seen driving off into the sunset — but we know that Pretty Little Liars happy endings don't come that easy. There's still two hours of mystery, twists and shocking developments to come before Pretty Little Liars is over. That means something will bring A.D. back to town and the girls have to be ready to take on their greatest foe ever.

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The penultimate episode went a long way to answering lingering questions, but the biggest one of all still remains. Who is A.D.?

Find out next week when the Pretty Little Liars two-hour series finale airs Tuesday, June 27 at 8/7c on Freeform.