[Warning: The following contains spoilers from Tuesday's Season 2 premiere of This Is Us! Read at your own risk]
Jack died in a fire that consumed the entire Pearson family home. We're not sure what started the fire or how it went up (though let's make an educated guess that it's something of Kate's that got the fire going, based on what we've seen of Kate's guilt over her dad's death).
The heartbreaking reveal came after Jack revealed to Rebecca (Mandy Moore) that he's an alcoholic and needs to fix his problem before he can return to her and the kids. She refused to take that from him though and insisted he get in the car so they could figure out a way to fix it. She promised in a few months that everything would be better.
The show then flashed forward to Rebecca driving the jeep alone with Jack's personal belongings in a ziplock bag on the passenger seat. She pulled up to the burned remains of their home and collapsed into sobs, seemingly confirming Jack must have died in whatever fire took down their house.
Does that really mean that Jack died only a few months after going to rehab or whatever treatment they find for his drinking, though? Not necessarily. Kevin (Justin Hartley) revealed in the present timeline that Jack died when the Big 3 were 17 years old. That makes it very ambiguous as to how much time had passed between Rebecca getting Jack from Miguel's and when the house burned down.
In typical This Is Us fashion, the reveal only leads to more questions than feelings of satisfaction. He died in a fire, but what started it? Why was no one else home? Was he drunk when the house caught fire and that's why he didn't get out? We'll have to stay tuned as more answers are revealed throughout the second season.
This Is Us continues Tuesdays at 9/8c on NBC.