Were you tempted to talk to any of your co-stars about it, about your idea of what was going on? Did Evan know?

I was so close with everyone that I didn’t want anyone to start treating me differently on the show. Not that the actors would fall prey to that, but I didn’t want them thinking, or considering the fact, or weighing the fact out. I didn’t discuss it with a single person. Not a single person. Also, Lisa and Jonah, when they say, “don’t say anything,” you don’t feel like they’re trying to box you in. You feel like, “This is probably best for everyone.”

What was the reaction like when everyone else found out? Did you then confer with Ed Harris about how your two different characterizations would converge?

I basically thought it was my task to learn from him. We didn’t work that much together—we were almost never on the set together. We had a little meal together with Jonah and Lisa and Evan on our last night. We were the last ones sticking around, and he gave me a wink and we talked briefly about our lives, and he gave me a pat on the back and he said, “I hear you do a good job.” That was beyond what I could ask for.

So you didn’t get to study him at all?

Jonah would give me clips towards the end of the season, when the audience would be able to see the two men together in William. He gave me some advance footage. But there’s 30 years in between, so I wanted to be truthful and still have there be a separation because we all change so much. But William starts leaning in, and Jonah helped me with that.

Were you surprised that some viewers figured the twist out after your very first appearance? From Episode 2?

I was stunned by the Episode 2 call-out. I was so surprised that after maybe the third episode, I wrote Jonah and Lisa and I said, “I know I overthink things, but HBO would like us to be a little bit active here on social media, and I’m responding to everything except the Man in Black tweets. Now, I‘m thinking, ‘Is that proving their case?’ Someone can easily collect that data and say, ‘Well, look, he’s not responding to these tweets.’ What do you think I should say?” And then Lisa wrote me back and said, “You don’t overthink things. That’s why we hired you, because you think like us. We were just planning our attack.” They sent us all an e-mail saying, ”You don’t have to avoid, but don’t lie.”

Who had the best reaction when you all found out officially?

Thandie [Newton]’s reaction was probably the best on set. I’m walking through set and I hear, “Yoooooooou!” She’s pointing at me smiling and she’s so tickled, because she had no idea.

You don’t get any scenes with Thandie, right, because of the timeline stuff?

No, but we both had a lot of time in Sweetwater, so we worked on a lot of the same days. There were often two units filming at once. She thought, “Oh, Jimmi Simpson is playing a sweetheart and he is one.” She just had no idea it was coming.

I was so delighted to see you cast as a sweetheart, because you’re often cast a little creepier. Were you dismayed at all to see that your character would go darker as the season progressed?

I wasn’t, because even before I was aware of the truth, there was a nod towards something in the audition. I read for Logan and for William. Logan was there on the page—funny, kind of sexy, sarcastic—and William was like his intro in Episode 2. But then there was also this scene of the same man, but turned cold. I can’t remember how they articulated it, but it was just the same man, and now they wanted to see him completely flipped around. It wasn’t violent and it wasn’t angry, but it was the same man with a completely different perspective. Of course, it was inevitable, but I was really just enjoying each day as it happened of not playing the Man in Black.