SPOILER ALERT: Do not read if you have not yet watched “Songbird Road Part Two,” the 12th episode of the third season of “This Is Us.”

The tragic story of Nicky Pearson came to a dramatic but open-ended close on the 13th episode of the third season of “This Is Us,” in an episode entitled “Songbird Road Part Two.” After the Big Three found their uncle (Griffin Dunne) with a pistol and a bottle of booze, they coaxed him into joining them at the hotel. Kevin (Justin Hartley), Kate (Chrissy Metz), Randall (Sterling K. Brown) and even Rebecca (Mandy Moore) attempted to get him some help. It was the first time the older Pearsons spent time with their uncle, and the first episode in which Dunne shared scenes with Moore. By the end of the installment the character hadn’t really changed, but he did agree to go to a meeting and to let Kevin fix the hole in his trailer’s roof before sending his family away.

“Nicky’s character isn’t really ever interacting with the same batch of characters; it’s two different worlds,” show creator Dan Fogelman tells Variety. This is why, he says, they cast two actors — Michael Angarano for flashbacks and Dunne to play the present day version of Nicky. “When he’s younger he’s only with Jack, he never knew the family. When he’s older Jack’s not alive anymore. We thought that gave opportunities the same way as with William [Jermel Nakia and Ron Cephas Jones]. And also Michael is just so inherently boyish and so much time has passed.”

Fogelman, who feels Dunne was a “perfect fit” in the role, adds that the plan was always to introduce Jack’s (Milo Ventimiglia) brother as alive down the line, and that one of the show’s consultants, Vietnam War writer Tim O’Brien, filled in the blanks as to what created a rift between the brothers when he co-wrote the first of the two-part episode.

“A lot of it is baked into the writing and there’s a plan for it and why,” he says. “We always knew Jack went to Vietnam, that Nicky got drafted and Jack enlisted to hypothetically be with him at the same time — and then found him and a dark thing happened that created a rift between them. That Jack, from that moment on, walked away from his family and from his brother. So that was always the plan and the details of what happened we found later.”

To dig more into creating the older version of Nicky, Variety caught up with Dunne. Here he breaks down his own sliding doors story of how he was almost drafted for the real-life war, how he and Angarano matched mannerisms, and whether viewers can expect to see more of him in the “This Is Us” universe.

When you were approached for the role, what was the pitch they gave you?

I got on the phone with Kevin Falls, who told me about this very complicated and kind of tragic character who was a family member. I’d been a fan of the show, and I knew they’d mentioned Nicky as being dead. So that was a terrific surprise. But they also told me that Tim O’Brien wrote the episode with Kevin. I was sold right there — not that I needed that much selling. Tim is a writer I’ve admired a great deal, and I’m also something of a Vietnam-ophile, having almost been drafted. I grew up with that war. I’ve read every book, non-fiction and fiction, about that war as far as I know. The fact that he wrote it, and to play someone with PTSD and a diabetic and an alcoholic and just having so much on my plate — a solitary, kind of tragic figure who was also actually over 10 years older than I am — I recognized immediately it was a fantastically rich and complex character.

What is the story behind almost being drafted?

I got a draft card when I turned 18 just like everybody else on June 8th would have gotten. I have to do the math what year it was, but I got the card and the number was pretty low. I took that to mean I had a pretty high chance of being drafted. But within a month they ended the draft system and ended up pulling troops out of Vietnam. But in an alternate life I’ve often thought what my life would be like if I was drafted. I found that war, growing up with it and watching it on television, just terrifying. In the jungle, and booby traps and snipers and the monsoons — it looked like I was never going to live through that. So Vietnam since has always held a fascination for me. I just imagined what could have been, which, thank God, was not.

How else did you get into the mindset of this character, whom viewers already have an intimate experience with from the younger portrayal?

I watched a lot of films, particularly one 1946 film about PTSD by John Huston called “Let There Be Light.” It was a documentary made about the war after World War II, when PTSD was called shell shock. It showed sessions between military psychiatrists and severely damaged young soldiers who were just rendered incapable of speaking. And just their inner life and what was going on behind their eyes and in their minds was something. I just brought my laptop very close to my face to look at their expressions and imagine their thoughts. I was playing a guy who suffered that as a result of the war and chose to live a solitary life and not speak to anyone except, say, somebody in a grocery store or liquor store. What that life would be like, to be silent and alone and the only person you talk to is yourself. It was a fun thing actually to sort of investigate that quiet inside your mind and then imagine what it would be like when that quiet is so disrupted by having the Big Three come, wanting things from me — making me talk, making me remember. And all the pain that would bring up of the past. I’d been trying to forget and take myself out of it.

What kinds of conversations did you have with writers or producers about that time in between viewers seeing Nicky and Jack’s last meeting and the moment in which the Big Three show up?

We definitely talked about that. They kind of left it to me to fill in my own backstory, but what they did say and what I followed was really a guy who is probably living off his veteran’s pension and just made trips into town for when he needed to do it. He probably gave a VA treatment center a shot, but it had no interest for him and had too much interacting with other people. He didn’t play checkers. It was another intrusion. He didn’t want to seek help. He was in self-exile, or self-punishment. He felt all this time like he just deserved to suffer. He probably got a trailer that was relatively new decades earlier and it just decayed like he has in all that time.

Did you question Nicky’s motivations for not reaching out to Jack again following their last conversation?

I think he was on the verge of doing it, and already in that scene with young Nicky you see what I was doing later on, which was that push-pull of wanting to connect but wanting to be left alone. And needing and then wishing you didn’t need. I think he was on the verge of maybe telling him what happened. But when Jack took out the pictures of his family and Nicky saw the life that would never be his and knew his brother had kept it from him? He compared himself to his brother’s life and his wife and children and particularly that house. … He always had a fantasy as a little kid of the kind of house he’d have — he talked about having two houses. And he really loved his brother, and his brother cut him off. That just welled up all that anger and rejection and he just did what I think was a very destructive thing, which people do when they’re angry and hurt, and he just sent him away. And chose to suffer for his sins on his own.

Tonally how did this experience stack up to previous projects?

It was unlike anything I’d ever done. I love that they thought of me for this. I’m not sure how they thought of me for this because the last major thing I did was playing a kind of screwy, neurotic academic in “I Love Dick.” It was a very comedic part. This part certainly was not. I think they wanted someone who has lived a life…which I certainly have done and continue to do. But there was a lot to draw from. Just showing age, experience, loss and all those things that exist in Nicky, I think that’s how they came up with me.

You played Michael’s father in “Snow Angels,” but what kind of conversations were you able to have in preparation to play the same character?

We didn’t really have time to talk about it, or match up our mannerisms. There was a little thing where we both picked at an imaginary scab on the same place on our arm, but it was kind of a stroke of genius to put us together. I think they found out afterwards that we had played father and son. I had the advantage of seeing Michael before I started working in his Vietnam setting, so I learned a lot from that. But it was kind of a thing where even both of us texted each other afterwards saying, “God we kind of reminded each other of each other.” It was what we’d hoped would happen, but we didn’t really have a moment to plan it.

It’s hard to imagine older Nicky having much reason to laugh, but Michael brought a distinct laugh to the character — is that something you’ve tried to emulate yet?

If I have a future here with Nicky and there’s a laugh in there I’m going to go back and definitely simulate it somehow. But a much older version.

Have you had conversations about Nicky’s future with the show?

It is open-ended. I read that there is talk of me coming back but I don’t know in what capacity or timeframe or anything.

“This Is Us” airs Tuesdays at 9 p.m. on NBC.