Pretty Little Liars series finale: I. Marlene King reveals her original idea for A.D.

Spoiler alert: This post contains plot details from the series finale of Pretty Little Liars.

After two hours of fake-outs and flashbacks, Pretty Little Liars finally answered the question fans have been asking for years: Who is A.D.? Turns out, it was someone named Alex Drake, or as the PLL fans prefer to call her, Twincer. Yep, A.D. was Spencer's secret (and very evil) twin.

It was Wren who discovered Alex in London, after which he told her all about her long-lost family in Rosewood. And once Alex connected with her half-sister Charlotte, she realized just what she'd been missing. But when Charlotte was murdered, Alex did the only thing she could think of: torture the Liars until Charlotte's killer was revealed. And after that worked, Alex came up with a new plan. She was going to kidnap Spencer and assume her identity. And it almost worked. But, in the end, the Liars got their happy ending, and it was Mona who walked away as the ultimate "A."

EW spoke with PLL showrunner I. Marlene King about the finale's big reveals and more.

ENTERTAINMENT WEEKLY: When it came to the A.D. reveal, how did the idea of Alex Drake come to you? Were there other ideas you couldn't make work?
I. MARLENE KING: Originally my mind was going to Wren as A.D., but we had to be realistic and there have been times when we really needed a character who wasn't a series regular and we couldn't get them on the show. The show is so deeply rooted in mythology and I've always said you have to know the ending before you know the beginning or else it won't make sense, so that dictated that we needed to make A.D. someone who was a series regular. I know a lot of fans wanted it to be one of the Pretty Little Liars, but I could never justify that being true because the show was always about their unconditional friendship. That then sort of led to this idea of, well, if we make it a twin of one of the Pretty Little Liars, that's sort of like making it a PLL, but ultimately, it makes more sense.

How did you pick which PLL got the twin?
We had already started the mythology about Peter Hastings sleeping with Jessica and then knowing that he accidentally slept with Mary, it just made so much sense. Even the fact that they've lived together since the pilot and those two families are just so intertwined, it made a lot of sense to make it Spencer.

So when did Alex start showing up in Rosewood?
As soon as Charlotte was killed, that's what motivated Alex to come to town. So although we didn't see Alex on screen until season 7, Alex was A.D. in 6B.

So Alex was the one who shot Spencer?
Yes.

Who visited Mona in a black hoodie at the start of the hour?
That was Wren.

That was Wren before he was made into a necklace.
Yes. [Laughs] Exactly.

I'm scared to ask about how Alex got him to father those babies.
We thought we had that actor for more days than we did. I had written a death scene, and in that scene that we never shot, he says to Alex, "I even created life for you." So Wren knew that he was the father of those babies.

Was there anyone you really wanted to get back that you couldn't?
We got Melissa. We really wanted to get Jason back. We couldn't get Jason. And we really wanted Mike, Cody Christian, and we couldn't get him back either. Both were busy on other shows. <iframe height="569" width="100%" scrolling="no" frameborder="0" src="http://renderer.qmerce.com/interaction/58ef7d70cb4fa68908179ed6?channelId=562ad32b495c869d5f960800" class="" allowfullscreen="" resize="0" replace_attributes="1" name=""></iframe>

I love that Mona ultimately won the game. How did that come about?
That was the entire writers' room brainstorming. We didn't just want to leave it on the sad goodbye. What's the twist on the twist that will get you excited? And I wanted Mona to live happily ever after, so we came up with that.

For you, what was the most difficult scene to write?
Definitely the girls saying goodbye to each other was difficult to write. I finished the script probably a month before I wrote that scene. It took me a long time to sit down. We were probably already prepping that episode and Lisa Cochran was like, "You have to write that scene, Marlene. Go to your office and write that scene." As a writer, that was my goodbye to the PLLs. It was a tough one.

I know they ended up together, but can you promise me that Toby and Spencer are getting married and are together forever?
Yes. I hope fans got that. We literally did say, could we have a double wedding? Or should we have a triple wedding? That felt like it was a little too much. But I think they got their happy ending.

The very final scene could be seen as the ending of our chapter or a beginning of a new chapter with a new generation of PLLs. Is that something you're thinking you'd like to explore?
Yes. I just love this town, and Rosewood is such a fascinating place. Not just myself but all the writers — even the studio and the network — we all loved the idea of saying, "This chapter ends but whether we ever see it on screen or not, the audience knows that the creepiness of this town continues."