This Is Us Creator Dan Fogelman Breaks Down Surprise-Filled Season 4 Finale — Plus What's Next

New faces and expanded storylines unspooled more details about the Pearson family’s future as season 4 of This Is Us closed out with the time-jumping finale, “Strangers: Part Two” — and just like Chrissy Metz recently told PEOPLE, “there’s a lot to unpack.”

In the present day, everyone gathered at Kate (Metz) and Toby (Chris Sullivan)’s Los Angeles home to celebrate baby Jack Damon’s first birthday. The event also marked the first time Rebecca (Mandy Moore), Randall (Sterling K. Brown) and Kevin (Justin Hartley) were together again after their tense New York trip.

During the party, and much to Kate and Kevin’s surprise, Rebecca announced that she had changed her mind and would be moving to St. Louis with her husband Miguel (Jon Huertas) for nine months. What she didn’t disclose: Randall guilt-tripped her into the Alzheimer’s clinical trial by calling it “an investment in her future.”

Meanwhile, in the past, Rebecca and Jack (Milo Ventimiglia) commemorated his big day (with the return of the Pittsburgh Steelers Terrible Towel birthday suit tradition!) as well as the Big Three’s first birthday with a small party and a reunion with their close confidant, Dr. K (Gerald McRaney).

As for those big revelations about the Pearsons’ futures, creator Dan Fogelman breaks down new details about the main characters and discusses where season 5 will pick up.

RELATED: This Is Us‘ Chrissy Metz Calls Season 4 Finale a ‘Doozy’ — ‘There’s a Lot to Unpack’

Rebecca

With an impending move to St. Louis, the matriarch has a “challenging chapter” ahead, according to Fogelman, who has already written the season 5 premiere.

Mitchell Haddad/NBC

“We have a big storyline planned for Mandy in the next coming season in present day as an older woman and her past timelines,” he says. “Particularly, when we land in St. Louis with her, kind of exploring with Miguel. … Here is the opportunity where we’re going to be bringing them in a location together and undergo this treatment that they didn’t necessarily plan on trying.”

Fogelman adds, “It will also allow us to get towards, which has always been the plan in the back part of our series, further understanding how their relationship bloomed then stalled then bloomed again and really getting inside their lives.”

Randall

The councilman was the only Pearson family member enthusiastic about the clinical trial, calling it “an investment in [Rebecca’s] future.” Those exact words would cause immense friction between him and Kevin, who confronted Randall for forcing their mother’s hand.

Ron Batzdorff/NBC

And years of pent-up frustration finally came to a head when Randall unloaded on his brother about their late father Jack. “He died ashamed of you,” he told Kevin.

In another low blow, the father of three compared the “shame [Jack] felt for [Kevin] and the pride he felt for me,” telling his actor sibling: “You’re not even chasing Dad’s shadow, Kevin, you’re chasing mine. You’ll never be him, and you’ll never be me. Because you’ll never know what it’s like to devote yourself to anyone other than yourself. You’ll pretend but it’ll just be a performance, tired, stale performance — like all of your performances.”

Fogelman explains, “Family rifts are really hard to both be a part of and to watch,” later adding, “It had to be something that would really separate these two for a period of time for this family.”

Kevin

Kevin, who was riding high on his one-year sober anniversary and the release of his nationwide cologne ad, did not take Randall’s verbal jabs lightly and delivered an equally harsh response.

“You know, I used to think the worst thing that happened to me was the day that Dad died. It’s the day they brought you home. Hand to God Randall, the worst thing that ever happened to me was the day they brought you home,” he told Randall, who — unbeknownst to Kevin — had just talked about Jack’s death and Rebecca’s past correspondence with biological father William to therapist Dr. Leigh.

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“This is Cain and Abel type stuff for these two, this is a fight that goes towards literally their inception,” says Fogelman in breaking down the intense fight. “Two kind of alpha men growing up under the same roof in the same exact period of time, both with widely different skill sets. Part of making a drama is not being afraid to make people be really flawed and really ugly so that hopefully, as we tend to do on our show, the hope and the repair we offer is well-earned and well-executed when it comes.”

But that was just the second conversation to impact Kevin’s future. Madison, Kate’s best friend who he slept with during a vulnerable period, stopped by baby Jack’s party to break the news to Kevin that they are expecting.

And surprise: she’s pregnant with twins. Fogelman reveals that Madison’s OBGYN will be “counseling” and “tending to a couple that doesn’t know each other very well on the cusp of having twins.”

As seen in the flash-forward, Kevin’s son and daughter join their gracefully aging father by Rebecca’s bedside with Randall, who received a supportive rub on the back from his brother in what could be a sign of unity. (Also: Uncle Nicky is sporting a gold wedding ring in that same scene!)

“There are many more chapters in Kevin’s romantic story,” Fogelman says when asked about the identity of Kevin’s future fiancée. “Kevin has a journey ahead of him.”

Kate

Along with hosting her son’s party and learning of her mother’s sudden St. Louis plans, Kate also had a full plate with a “secret special thing” to do with Toby and their birthday boy.

Ron Batzdorff/NBC

Though her family members didn’t seem to acknowledge it, the Damons were excited for their visit to the Los Feliz Medical Center’s NICU where they pinned a family photo on the wall of fame to mark the success of baby Jack’s milestone year. While there, Toby proposed the idea of adopting a sibling for Jack after being swept up by the emotion of the happy day. “Doesn’t Jack deserve that? Doesn’t he deserve someone to spend his childhood with?” Toby asked Kate.

Fast forward to the future and audiences were introduced to Hailey (Adelaide Kane), an art curator, who may be hung up on a movie star after a one-night stand. Turns out, Hailey is Kate and Toby’s daughter, who seemingly has a close relationship with her brother (Blake Stadnik), who welcomed a daughter named Hope with his wife Lucy (Auden Thornton).

However, neither Toby nor Kate showed up to the hospital to meet their granddaughter.

“Our hope is to continue to make people invested in the future storylines by getting to those characters slowly, as we’ve done, so that by the time we’re really landing to full stories with them, if we do, you feel that great investment,” Fogelman says.

NBC

Jack

At the time of the Big Three’s first birthday, Jack and Rebecca also remember their late son Kyle. As the couple continues to grieve his death, they mark their kids’ birthdays with a surprise visit to Dr. Nathan Katowsky’s office for some guidance and comfort — the physician’s previous advice had a “sizable impact” on their lives, and Dr. K also lost his first child.

Speaking of the “human experience,” he told Jack and Rebecca: “I think the trick is not trying to keep the joys and tragedies apart but you got to let them cozy up to one and another, and co-exist. I think if you can do that and manage to forge ahead with all that joy and heartache mixed up together, never knowing which one’s going to get the upper hand, then life does have a way of shaking out to be more beautiful than tragic.”

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Since the series debuted in September 2016, the Pearson family tree has become significantly larger.

“It’s always so interesting to look at the kind of matriarch and patriarch of a family, like Jack and Rebecca, and start with them simply on a bed with Milo sitting with a Terrible Towel covering up his junk, and then realize decades later there will be all these human beings that are all shoots of these people, both biologically and emotionally through adoption,” Fogelman says. “Doing it in an elegant and slow way where you know where we started with a guy and a girl on the bed and we ended with this giant fabric of life was always something we hoped to execute by the time we’re done.”

As fans have come to know, each season premiere starts with the Big Three celebrating their birthdays. When the fifth installment kicks off with their 40th birthdays, Kevin and Randall are not on speaking terms following the fallout of their verbal blowout.

Of next season’s themes, Fogelman says, “I’m very excited about, especially with where the world is right now, the uplift, and I would call it almost rebirth, that comes next season. Kind of rebirth and a lot of new beginnings, particularly for birth and rebirth would be a big thematic part of next season.”

The showrunner also teases: “There’s going to be something big in the season premiere.”