'This Is Us' Reveals Why Jack Is an Old Man in Bittersweet Season 2 Finale

Fans' questions about the return of the Pearson patriarch were answered in heartbreaking fashion in Tuesday's finale.

Warning: Spoiler alert! Do not proceed if you have not watched Tuesday's finale of This Is Us. If you have, make sure to read all about the new season three mysteries the sophomore finale introduced.

The mystery of old Jack has been answered.

Over the last week, fans of This Is Us have theorized over why, in a recent preview, Jack was seen in all his salt-and-peppered, bespectacled glory, seemingly happy and healthy, even though it's been established that Papa Pearson died years ago. In Tuesday's finale, there was no Lost twist or supernatural revelation explaining Jack's old age. And no, Jack didn't fake his own death only to return to celebrate "Katie girl's" wedding day. Turns out, the presence of old man Jack was in dreams Kate had been having of what the Pearsons' lives should have been.

So, how did Kate envision the Pearsons' "What if" reality had Jack not died?

In her dream, it's Jack and Rebecca's 40th wedding anniversary, and friends and loved ones have gathered together at the family cabin to stand witness to the couple's vow renewal ceremony. Everyone in the Pearson family is there for the most part, save for Toby and Miguel. During the vow renewals, Jack is about as perfect as you could imagine, telling his wife just how lucky he is to have her by his side as partners in Big Three Homes, the construction company he once dreamed of opening.

“Some of you may not know this, but for the 22 years that I worked for Lundy Builders, my wife put a folded note packed into my briefcase every day. The highlight of my day in the office was opening one of those little scraps of paper," Jack tells Rebecca and their gathered loved ones. "When Rebecca and I started Big Three Homes, she stopped writing the lunch notes, but I was OK with that. I had the highlight of my day right there, sitting by my side every day.”

Kate also dreams the reception for Jack and Rebecca's vow renewal ceremony, where Rebecca performs their song, "Moonshadow," the same ballad she was singing the first time her husband laid eyes on her all those years ago. “Long before Jack and I had our own company, and long before the Big Three were around, I was singing in a bar and a man walked in," Rebecca introduces before singing the gorgeous Cat Stevens tune, the memories of which cause Jack to get emotional and wipe away a tear. There are even vignettes of Jack dancing happily with Rebecca and Kate.

There were small clues over the course of the episode that all of the moments shared between Jack and Rebecca were figments of someone's imagination, and it made the most sense that it would be Kate, as she likely still harbors lingering guilt over playing a small role in Jack's death. It's confirmed though when Kate confesses to Rebecca on her wedding day that she's been "having dreams" of what "it was supposed to be" for them.

“We’re at the cabin, at a wedding, but it’s not me and Toby, it’s you and Dad and you’re renewing your vows. And you’re so beautiful and Dad is older and grayer, but still Dad," Kate admits to her mom over the phone. "We’re just all there and we’re so happy together. You know, the way it was supposed to be." Rebecca assures Kate that her dreams are completely normal, telling her that the visions sound "really beautiful."

"Weddings can be really emotional. They stir all kinds of things up," she says, calming her daughter, who begins to second-guess why Toby isn't in her dreams to begin with.

Kate eventually drives to the tree stump near the family cabin, the same one where she and Jack often shared father-daughter moments when she was younger, taking Jack's urn out of her purse and setting it beside her. She reflects on the summers she spent at the town carnival, riding the roller-coasters with her dad, "feeling so scared, but so safe, all at the same time," before deciding that it's time to let go of Dad. "I've been holding onto that feeling for a really long time now, that feeling of you next to me. But Dad, I'm getting married today -- and I've got to make room for Toby, so I've got to let go a little now." Though we don't see her doing it, it's alluded to that Kate pours out the rest of Jack's ashes when Randall asks, "So... you did it?" and Kate responds content, "I did."

Kate's actual wedding to Toby overlaps with a flashback to the past when young Kate innocently asks Jack if she could "marry" him one day and he sweetly tells her "that's not really how it works." But really, Kate's sentiment is understood; she wants to find a man comparable to Dad. Jack's response is about as heartwarming as one can get, but also heartbreaking, because he's unable to fulfill his promise to his only daughter. "The guy who gets to marry you, Katie girl, your mom and me, we’re going to be there, check him out, make sure he’s as good at board games as you think that he is. And assuming that he is, I’ll get to walk you down the aisle and I may even cry a little," Jack says to young Kate. In a sense, his presence is felt, just not the way Kate would have thought.

Later, Kevin gives a toast at Kate and Toby's reception and may as well have been talking to viewers of This Is Us, who, up until this season, had been holding their collective breath over the mystery of how Jack died"I think we’ve all been holding our breath for a long time..." Kevin says to Rebecca, Kate and Randall. "I think that the four of us should release that breath together. I think it’s important that we do that, that we let go of the things that we’ve been holding onto.”

Ahead of Tuesday's finale, Milo Ventimiglia revealed that the presence of old Jack in the season two finale is a rare occurrence and not to expect that iteration of the character to return in the future. "I feel like that's maybe a one-time thing. It's only once in your life, like a blooming flower," Ventimiglia said, adding the experience of being aged up was "a lot." "But you can't help but feel like you're in your 70ish years when you're in it. We were in between scenes and I was talking to someone and how [I was] standing, I couldn't get out of 70-year-old Jack."

Reacting to the old Jack and Rebecca scenes, Mandy Moore called their finale moments "a beautiful way to punctuate the end of this season." "It sort of makes you wistful for what could have been," she said.

What did you think of the season finale of This Is Us? Tell us your thoughts by tweeting your thoughts to @etnow!

This Is Us returns this fall on NBC.