These stories don’t get much better than this: The late maternal grandfather came from Jamaica to Brooklyn and cheered for Patrick Ewing and … well let his son-in-law tell it.

“I used to sit and watch the Knick games every time I went over, especially when I was courting my wife,” Rowan Barrett told The Post after his son and Noel Duhaney’s grandson, RJ Barrett, was selected by the Knicks with the No. 3 pick in the NBA draft Thursday night at Barclays Center. “He was obviously of Jamaican descent and he loved Patrick Ewing: That was the only team in the universe that existed to him, right? And so this was his team, and he would tell RJ, ‘One day you can play for this team.’ Like he’s trying to help him have dreams — right? — as a young guy.… And wow, look at it today, he knows, he’s very well aware this was grandpa’s team.”

So grandpa’s team becomes RJ’s team, and if father knows best, the Knicks knocked it out of the park. Rowan Barrett was asked what he would tell fans about his 19-year-old son, who was 3 months old when the Knicks traded a 38-year-old Ewing to Seattle.

“That he’s tough … and then he’s a competitor,” Rowan said. “But also that he’s young. … I think he plays to win, and I’ve never seen a time where he’s had trouble in a locker room. He’s been a leader in almost every environment he’s been in. Obviously now he’s gonna be playing with men, right? And now you’re gonna have to figure it out, he’s starting from the bottom, he’s starting from nothing, and all that other stuff he did really doesn’t matter now. You’re now coming into a league to a team with men, and how are you gonna gain their trust? But as I said, he’s got a competitive spirit, he loves to win.”

His son, a silky smooth 6-foot-7 athlete, loves the bright lights and the big stage, just as Rowan Barrett, now general manager of the Canadian men’s national team, did when he left Canada to play for St. John’s.

“That’s the reason I chose New York initially,” Rowan said. “I was coming from Canada, and we didn’t really know much at the time, and we thought, ‘OK, if you can perform here, you can perform anywhere.’ We didn’t really understand much about the States, so we said, ‘OK, it’s most difficult there, let’s go there.’

“He has a little bit of that in him. He thrives on challenges, it’s kinda his thing because he’s so competitive. This will be a gargantuan challenge, New York City. But I like the fact that he wants to swing for the fences. Let’s see where the chips fall. If he succeeds here, it’s gonna be because who he is and how he works. And if he doesn’t, it’s not gonna be because of any lack of trying or anything mentally or anything like that.”

Rowan, a 6-6 guard/forward, never made the NBA, but played all across Europe. It helps explain RJ’s maturity.

“I think that our lives helped to bring that along,” Rowan said. “We lived in many different countries. He’s gotten to see all types of people and to walk in all types of cultures. He speaks more than one language.… He didn’t start going to school in English until the ninth grade, for example. He’s made friends with all types of people, all races — it’s all the same to him. I think that helps you to be a little more worldly.“And then secondly, we did things to prepare him. When he said that this what he wanted to do,” Rowan said, and smiled. “I had him in front of the television with a fork in the family room and my wife and I were drilling him with questions: ‘Can you tell me about the loss tonight? Can you tell me why the team lost? Why didn’t you help the team?’ Pushing it out of him, and helping to figure out how to compose himself.”

Of course there were hiccups. RJ cried himself to sleep homesick on occasion when he chased that NBA dream at Montverde Academy in Florida.

“You’re 15 years old and you leave home,” Rowan said. “His mother was injured at the time with her knee, so she couldn’t come down. Just imagine not seeing your mother from September till February in a boarding school. But he had his goals, he had his dream, and he’s going after it.”

And nothing and no one was about to shatter it. RJ is as mentally tough as they come.

“We put him through a lot,” Rowan said. “I sought out the most difficult coaches to coach him. When he was 12, I almost pulled him from a team because the coach wouldn’t yell at him, out of respect for me. I said, ‘I brought him here for this reason. Get after him!’ He said, ‘Well, are you sure? Maybe I gotta build a relationship.’ I said, ‘What relationship? He’s 12, tell him what to do, he’s gonna do it.’ ”

And RJ did it. When the boy was asked what he admired most about his father, RJ said: “Work ethic. My dad’s a very hard-working man. More than anybody will ever know.”

It was an emotional day, tears of joy for Noel Duhaney’s grandson. Somewhere up there, grandpa is smiling.

“That was one of the reasons why I was crying, because we used to watch the Knicks growing up and he would always tell me I was going to be a Knick,” RJ said in the interview room. “I’m sad he can’t be here to see it. But I’m just very happy, man.”

The Knicks should be too.