Patient This Is Usfans were finally rewarded Tuesday night when the NBC drama shed some light on Jack's (Milo Ventimiglia) trauma in Vietnam. More importantly, the audience learned why the seemingly unflappable Pearson patriarch lied to his family about the death of his little brother, Nicky (Michael Angarano).

But first, a little recap: It was confirmed in the winter finale that Nicky was not only still alive, but that he was living just a few hours outside of Pittsburgh. The winter finale also revealed that Jack had known his brother was alive as late as 1992, six years before Jack died. Tuesday's episode, "Songbird Road: Part One," explained what happened in Vietnam from Nicky's perspective and what caused the irreparable rift between the two brothers.

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Remember the little boy with the infected foot that Jack made Nicky tend to? Shortly after that, Nicky took the little boy out on his boat to go fishing. High as a kite, Nicky decided to use grenades to catch the fish. After he dropped the first one in the water, he went for a second, but the little boy wrestled with him for it and accidentally pulled the pin, activating the grenade. It dropped in the boat, and Nicky tried to get the kid to jump into the water with him, but the kid hesitated. Nicky made it into the water, away from the explosion, but the kid was blown up along with the rest of the boat.

Jack was the first person to reach Nicky, but when he saw that an innocent kid had died at the hands of his reckless brother, he was done. It was too egregious of an error in Jack's moral code for him to forgive. Nicky was sent home from the war for psychiatric reasons, and Jack let him go, determining that Nicky was dead in his mind.

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Old man Nicky (Griffin Dunne) told the story to the Big Three, who took a road trip to see him after Kevin (Justin Hartley) showed them the postcard he had found in Jack's belongings. The flashback to Vietnam was intercut with Jack going to see Nicky in 1992 after he received the postcard that Kevin would find later. The purpose of the trip was to tell Nicky to stop sending postcards to the house, to confirm that their relationship was over. He refused to let his brother explain what really happened on the boat — that it was an accident — and Jack left him there in the cabin to grow old and die alone.

Milo Ventimiglia, <em>This Is Us</em>Milo Ventimiglia, This Is Us

The Big Three almost made the same mistake when Nicky dismissed them after learning how Jack died. They made it to a convenience store to buy more snacks for the road trip, but instead of heading back to Pittsburgh, they went back to get their estranged uncle. It was just in the nick of time, as they found the forlorn and devastated old man sitting at his kitchen table with an old pistol in front of him. Had they wasted any more time, Nicky would have killed himself over the guilt of never being able to tell Jack he never meant to hurt the kid.

What does this mean for the Pearson family going forward? Well the name of the episode, "Songbird Road: Part One," means that the show is definitely not done with Nicky or his story as it relates to Jack. He'll have to face Rebecca (Mandy Moore) next, who, after skipping the road trip, is now anxious to find out how her allegedly perfect husband could keep such a huge part of himself a secret from her.

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The Pearsons as a family will have to figure out how their image of Jack is changed by Nicky's story. For more than two seasons, he's been a larger-than-life figure who has almost haunted them with his passing. Finding out, and subsequently coming to understand, how Jack could turn his back on someone he swore to protect will permanently alter their world view and their idea of who their father was, which has been a central part of their being since the show began.

It's the move that This Is Us has needed to make since Season 1, when Jack became a martyr of sorts. Even when he did things that were not great or gave in to his vices, he always rebounded with a great speech or an out-of-this-world romantic gesture that made the cracks in his demeanor disappear. The revelations about the rift between Nicky and Jack finally makes the latter feel like a flawed human rather than the picture of a perfect father and husband. He was a man with demons and regrets who did not always have the answers — and that's a very interesting story to get to explore.

This Is Us continues Tuesdays at 9/8c on NBC.