Stephon Marbury in a scene from the documentary "A Kid...

Stephon Marbury in a scene from the documentary "A Kid from Coney Island." Credit: Andy Chan

Maybe this is a spoiler alert, but by the end of “A Kid From Coney Island,” the kid seems grown up, and at peace, neither of which one could see coming for much of the film.

Such is the journey of Stephon Marbury, one-time Brooklyn basketball wunderkind and later a mercurial Knick, who in a decade playing in China reinvented himself and his outlook.

The documentary about him, which premiered at the Tribeca Film Festival last month and still is in search of a distribution deal, chronicles it all through extensive archival video and interviews with relatives and friends.

About the relatives . . . Marbury is from a large family that included three older brothers who were standout players and a father, Don, who was an outsized figure on the local basketball scene of the 1980s and '90s.

“Somebody said, ‘Y’all doing a basketball documentary?’” co-director Coodie Simmons said in an interview with Newsday. “No. It’s a family story, from his brothers to his sisters raising him to his mom and dad and then going to China and creating a whole new family.”

It always was complicated, not least because Stephon was the family’s best hope to reach the NBA and help alleviate some of the challenges of life in Coney Island.

“He wore the pressure on his back, like a soldier,” co-director Chike Ozah said. “He felt like when he got to the league that it wasn’t just those few years of his teenage sacrifice that got him there. It was everybody before that who was trying to make it. He wore that like armor. I believe that was his drive.

“I couldn’t imagine what it would be like to be in his shoes. I don’t think I’ve dealt with real pressure. The worst pressure I felt at his age was probably cramming for an exam.”

Marbury, 42, appeared on the red carpet at the Tribeca premiere and told NY1 he considers his story one of “Triumph. That’s the word that I would use. I went through a lot, with a lot of adverse times, put myself in some up-and-down situations, and then here I am right now."

Of particular interest to Knicks fans will be the segment on his parts of five seasons with the team, including a toxic relationship with coach Larry Brown in 2005-06.

Don Marbury died shortly after attending a Knicks game in 2007, a loss from which his son struggled to recover.

“He was actually the backbone of that family,” Simmons said of Don. “We unfortunately couldn’t interview him, but from the footage that we researched we got to see how much he was a staple in that family.”

Simmons and Ozah directed “Benji,” about the late Chicago basketball star Ben Wilson, which debuted at Tribeca in 2012. Simmons said he felt Don Marbury’s spirit in this film the way Wilson’s animated that one.

Ozah said the directors were amazed at some of the footage available, including from a local TV station that spent a week following Marbury when he was at Lincoln High School in Brooklyn.

“We’re sifting through big, old beta tape machines that are collecting dust,” he said. “The stuff is priceless. We’re sitting here thinking, ‘Even Steph has never seen this stuff.’”

Simmons said the directors’ focus was more on making a film for the family, with the hope that others would find it interesting, too.

“Doing this documentary, it reads like a screenplay, like a really, really good screenplay,” he said.

With a happy and hopeful ending.

“There’s something special about 'A Kid from Coney Island,' where he came from to where he’s at,” Ozah said. “I can’t think of too many people who share that, who have two statues in another country.”

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