Warning: Spoiler alert! Do not proceed if you have not watched Tuesday's episode of This Is Us.

This Is Us may have wrapped up Nicky's story (for now), but, as a result, it opened an old can of worms.

After Kevin did everything possible to get uncle Nicky help, the closing moments of Tuesday's episode, "Songbird Road: Part Two," saw Kevin return to the bottle in a heartbreaking step back for the Pearson sibling. The recovering alcoholic took his first swig in months after Nicky failed to accept Kevin's consistent efforts to help him better his situation, something Jack failed to do when he was still alive.

The decision to have Kevin relapse was a crucial one for starJustin Hartley and the creative team behind This Is Us, who explained why they felt it necessary to have him go down this path yet again. The show spent a large part of season two exploring Kevin's alcohol-and-pill-induced downward spiral, especially after it appeared Kevin had turned a new page for much of the current season.

"We always try to approach our storylines with truth and honesty, and for so many people who struggle with addiction, it's not a one-and-done process. You do relapse, there are setbacks. We wanted to capture that," co-showrunner Isaac Aptaker told ET before addressing concerns that they are repeating themselves creatively. "You don't want to be repetitive when you're doing a TV show, but, at the same time, you want to be honest, and it felt so truthful to us that when he's at this emotional crisis, he would backslide and he would turn to alcohol to get through it. It felt very real, which is always what we strive for."

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"We're very conscious of it. You're going to see things unfold a little differently," co-showrunner Elizabeth Berger promised to ET. "Last season was very exciting because we did our big group family therapy scene, and that was cool to do the big, 11-minute scene with our entire cast, which was a very specific approach that we took. We're not doing that this time. He's going to be approaching his recovery from this in a completely different way."

As Hartley tells it, he was initially "surprised" by Kevin's life-altering decision, but echoed Aptaker and Berger's sentiments about the reality of the rocky journey one can take to maintain sobriety.

"It happens. It's sad," Hartley told ET. "I thought it was really sudden, so I was surprised, but at the same time it's not something that doesn't happen to good people. He's doing a lot. He's fresh out of rehab and decides it's a good idea to get involved and have a girl move in with him and fall in love. He's not giving himself to have time to take care of himself. He's set himself up for that without him knowing it."

There's a moment at the end of the episode when Kevin and Rebecca are in the car, heading home after Nicky promises to go to one Alcoholics Anonymous meeting. Kevin has the chance to tell his mom the truth about his relapse, but chooses not to. Kevin keeping his struggles to himself will be a throughline the show will investigate more thoroughly.

"Kevin's in a very different place in that in the new romantic relationship he's in, he's dating someone who has a lot of trust issues, who really builds walls and was very, very, very slow to let Kevin in," Aptaker said, referring to Kevin's romance with Beth's cousin, Zoe. "Betraying her and disappointing her has really high stakes to it."

"Even though there shouldn't be because it's such a normal part of the process, there is a lot of shame that comes with relapsing," Berger added. "You're going to see him dealing with that feeling of, 'Oh, my god, I can't believe that I'm here again. I've already put everyone through this one time. Now I have this woman I love and I have to put her through this.' We're going to see all of that at play going forward. You can make these great strides and then one thing can happen, or you can have one weak moment, where you're brought to your knees and all of a sudden, history is repeating itself. We had to show that cycle in order to tell Kevin's whole story as truthfully as possible."

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Was Nicky's rejection of Kevin's help the catalyst for him to turn to the bottle? Hartley and Berger mused on whether they agreed with that observation.

"I think so. I don't even know if it was that necessarily, as much as it was seeing where he was and how his dad left him and the disappointment and the anger that he had about his dad, this unresolved thing that he'll never get the answers to because he can't talk to his father. I think that's what it was," Hartley explained. "He got overwhelmed and didn't have anyone to call and talk through it. It's that feeling of being alone and desperate."

"Going to Vietnam and reconnecting with his father's past and discovering his uncle, it was all such an incredible journey for him. When you go on a journey like that, you fantasize what the happy ending is going to be," Berger noted. "In his mind, he hoped this would end with this beautiful, cathartic reunion. Obviously, it didn't quite play out that way. The devastation of that really caught him off guard and led to this weak moment of relapse."

While the sophomore season saw Kevin go to the depths of his addiction, Hartley hopes his character didn't fall into the trappings of alcoholism for a second time.

"I am too! I like my job too," Hartley quipped, offering his own advice for Kevin. "He's gotta open up and let people in and just spill it all out there and say, 'This is what happened. This is where I am and I need help.' He's got people around him that will help. There's no one around him that will be like, 'Eh, we're good." He's got his mom, his sister, his brother, Toby, he's got other friends, Zoe. These people will help him and they're good people. He's earned their help, I think. He's gotta do that but he's gotta be brave enough to do that."

Asked specifically who he'll turn to, Hartley offered this tease: "He's going to lean on his family and Zoe."

Melanie Liburd, who plays Zoe, hinted that if and when Kevin breaks the news to her about his latest struggle with his alcohol addiction, that she could very well be the one holding his hand throughout the process.

"She understands very well that he's an addict, and she's smart enough to realize that addicts can relapse," Liburd told ET, adding that Kevin has "evolved as a human being" since his season two struggles. "With Zoe, she's committed to Kevin. Whatever throws at them, they'll talk about it and they'll work it out if they can. She's a supportive girlfriend and she loves him."

Liburd revealed she was "absolutely devastated" when she read the script, but said it's an "understandable" situation. "He's taken on all this stuff, and he has a fragility to him, which is so sweet and heartbreaking to him. This has taken a toll on him," Liburd said. "What was so awful was they talk on the phone but he lies... ooh, she just wants him to talk to her and I'm sure she'll support him all the way."

Should audiences be worried about the status of Kevin and Zoe with this new development at play? "You should!" Hartley said. "You worry about everybody."

"Zoe likes the truth, so they're going to have to have an open communication to definitely get through and help him on his recovery," Liburd said, holding a slightly more positive outlook. "They're so sweet together, so I hope that he's OK."

This Is Us airs Tuesdays at 9 p.m. ET/PT on NBC.

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