[Warning: The following contains spoilers from the series finale of Pretty Little Liars. Read at your own risk!]

Now that fans have had a little while to process everything that happened in the Pretty Little Liars series finale, it's time to reflect and pick up on all the clues that A.D. was among the girls the entire time. In the end, it was Spencer's (Troian Bellisario) forgotten twin sister Alex who donned the hood and tortured the girls to find out who killed Charlotte (Vanessa Ray).

If you go back, the signs were there all along that a twin was the one causing all the havoc, but did you pick up on it? TVGuide.com talked to Bellisario on becoming the show's big bad for the final seasons, what it was like filming Alex and Wren's (Julian Morris) relationship and what fans need to know to really tell the difference between Spencer and Alex in those crucial scenes. Oh, and of course, which spin-off she'd like to return to.

Troian Bellisario, <em>Pretty Little Liars</em>Troian Bellisario, Pretty Little Liars

How is the day after this finale going?

Troian Bellisario: It feels a little like I'm hungover. I'm trying to think if I have less nerves now or more nerves. It was really nerve-wracking leading up to it because I had no idea how people were going to receive it. I think it's an interesting situation because now that it's done I'm just trying to process letting go of an experience after eight years and my own feelings, thinking about my life post-Spencer Hastings. I'm trying not to get caught up in the world of, "Did people like it? Do people not like it?" because I think it's going to be divisive either way. I've seen a lot of fan support. It's been awesome and people have had a great time. I've seen some people that were real pissed. Because I'm going through my own emotional goodbye to the show, I'm really just trying to breathe it in and enjoy the goodbye.

Speaking of enjoying things, what was it like for you to play the villain?

Bellisario: It was a total blast. I've been dreaming of doing that the entire time on the show. When Marlene told me that we were going to be able to do it and then when I was able to do it, it was like a dream come true. I was so happy bouncing back and forth, embodying Spencer and then embodying Alex. Everybody else seemed to be having a really fun time with it too. I just felt so lucky to be given that opportunity. It was a great way to spend the last couple of weeks on set.

Pretty Little Liars: The 5 Biggest Hints at A.D.'s Identity

I. Marlene King [creator] told me this morning that you purposefully didn't want any of the other girls to know [you're A.D.] so they wouldn't know when you were Alex and when you were playing Spencer. Who was the first one to figure it out?

Bellisario: No one figured it out! We were all on a night shoot and we were talking with no one around. Finally, one of [the girls] was like, "Does anyone know who A.D. actually is?" I just kind of tried to stay quiet. I think Shay looked at me and goes, "Oh my God, Troian knows! Troian totally knows!" and I was like, "No, no no. I don't know!" Then they said, "You have to tell us!" So that night I ended up telling them. It was funny because that was the night Ashley was like, "Wait a minute. You weren't Spencer in that scene with me when I was dreaming of you?!" I said, "No, that's actually Alex," and she's like, "What?! I feel so betrayed."

There are going to be fans that go back and rewatch this last season and a half to try and pinpoint the scenes where you were Alex versus Spencer. Do you have any tips for them on what to look out for and things you consciously did to separate Alex from Spencer?

Bellisario: There are a lot of tells. When you see her in the different scenes before the finale, she's learning. I was really worried about that scene when nobody knew about the twin and she came back to ask Toby for a kiss goodbye before he was going to leave with Yvonne. I was worried because she's impersonating Spencer's style so it's a really bold Season 1 Spencer sweater. She's really nervous and she hasn't really quite mastered the accent so it's a little bit of a tightness in her. It was funny because I thought people were going to see this from a mile away. Because people at that point hadn't known anything about the twin or seen any hints dropped about the twin, they just assumed that Spencer was just really nervous to be around Toby. So it's going to be fun for people to go back and see.

A Fond Farewell to Pretty Little Liars

What was it like for you to play out that really twisted Alex and Wren relationship? It seemed like they had a crazy saga we only got to see a few moments of.

Bellisario: I know! It's such a bummer because I loved them as a couple. They were so fun. Unfortunately, Julian [Morris, Wren] was supposed to be in much more of the episode. He had another work commitment so we only got him for one day so we had to squeeze in all these different scenes. Those were the first scenes I ever filmed totally as Alex in the one day. The scene where he shot me and the scene where he met me and the scene in the airport again but a different angle.

It was a whirlwind, but what we saw in them as a couple which was so wonderful was they had so much passion for each other. I think about that Romeo & Juliet quote, "These violent delights have violent ends." If you love somebody that much to the point where you're willing to hurt them, then there's no going back. Ultimately, in Alex's mind, she really never would have hurt Wren but she had to kill him. Each villain has their own morality. That's her morality, "I could never have hurt him. I loved him too much, so I ended his life."

Honest opinion time. Ash diamond necklaces: Sweet or creepy?

Belisario: My honest thought? Creepy as all get out, but Alex thought it was cute.

The Pretty Little Liars Cast Is Already Down for a Reunion

How many secret children do you think Mary Drake had?

Bellisario: Fortunately, it was only us three. I don't know! Maybe there will be a whole new saga that Marlene will spin off. I don't want to say. That's more a question for Marlene. Maybe Mary Drake had a lot more secret children but as far as I know, there are only three of us.

Do you think that Mary got the ending that she deserved?

Bellisario: I think Mary wanted a family and in the end Alex wanted a family. Mary and Alex got to live together and be mother and daughter. In a way, in Mona's twisted warped world, she's giving Mary and Alex a happy ending. They are not rotting away in secret jail cells, unable to ever see other people or feel love, but they have each other. Both of them, their whole life, wanted to feel like a family. In a weird way, it's a twisted happy ending.

If Freeform gave Marlene a PLL spin-off, which one would you rather make a cameo appearance on: a Mona spin-off or PLL: The Next Generation?

Bellisario: Janel is so good, I wouldn't pass up doing more scenes with Janel. I'm sure The Next Generation would be awesome and it would be great to have them, but Janel is so much fun to work with. I wouldn't pass up an opportunity to work with her.

Pretty Little Liars: I. Marlene King Spills on That A.D. Twist and Potential Spin-Offs

Would you do it as Spencer or Alex?

Bellisario: Both! Why not?

Do you have any lingering questions about Pretty Little Liars?

Bellisario: Obviously, how did the moms get out of the basement?! That's the ultimate mystery.

Check out our interview with series creator I. Marlene King about the happy endings, tapping Bellisario as A.D. and what she sees as the next chapter for Pretty Little Liars.