Warning! The following contains spoilers for the This Is Us episode "The Car." Read at your own risk!
This Is Us may have shown Jack's death already, but the show is nowhere close to done with stories about his life. Jack was back again in flashback sequences during the episode "The Car," and with Jack's appearance came another answer to a big question regarding his past. For the first time since fans discovered Nicky Pearson existed, Jack mentioned his brother in a conversation with Randall and Kevin and revealed that Nicky died while the two were serving in the Vietnam War.
Fans had assumed this was the case given that Nicky had only been brought up early in Season 2 and has not been seen in the present day, but there was still a sliver of hope by a few optimists that Jack's brother was alive and well somewhere. From what we can know from the episode that revealed Nicky, Jack served in the same unit as his brother in Vietnam and was likely there the day his brother died. Actor Milo Ventimiglia had mentioned in recent interviews Nicky Pearson's story would be explored further in This Is Us; judging from the sizzle reel that aired at the episode's conclusion teasing what's to come in future episodes, it looks like we'll see Nicky sooner rather than later.
A brief clip in the sizzle reel showed Jack and others decked out in army uniforms on board a helicopter, which means This Is Us is headed to Vietnam. Fans should be excited for this storyline as, in addition to telling a portion of Jack's story that Milo Ventimiglia has wanted to tell for awhile, it will tell us more about one of the major parts of Jack's life he doesn't talk about. Obviously, the death of Nicky hurt Jack deeply, and while we can only speculate, it might be the reason why Jack's issues with alcohol first began.
Nicky storylines likely won't just bring us to Vietnam. Jack's brother was probably present for a lot of Jack's upbringing, which is another topic the Big Three's father has never talked about. From what little we've seen of the two interacting, we know Jack and his father had a bad relationship. Stories with Nicky may further explain that divide between Jack and his dad. Jack mentioned to Kevin and Randall during "The Car" that he and his brother grew up needing to watch each other's backs, so obviously things were a little rougher for the two than it was for most children.