Former Met Keith Hernandez speaks during a Q&A on his SNY...

Former Met Keith Hernandez speaks during a Q&A on his SNY special prior to a game against the Astros at Citi Field on Tuesday. Credit: Jim McIsaac

Keith Hernandez enjoys history and has seen many documentaries in his time. “You know: Hank Aaron, Willie Mays, Marlon Brando, really any walk of life,” he said.

But not long before Tuesday night’s Astros-Mets game at Citi Field, Hernandez experienced something new: a documentary about him.

It is called “He’s Keith Hernandez” and will premiere on SNY at 6:30 p.m. on Wednesday, part of the leadup to the Mets retiring his No. 17 on July 9.

“It’s kind of surreal,” Hernandez told Newsday after the pregame screening. “I look at it and I see myself as a little 8-year-old and, you know, it's nice.”

The documentary is an hour long including commercials, so it is a Cliffs notes version of his eventful life and career, with a rich mix of video footage ranging from his Little League days to his appearance on “Seinfeld” in 1992 to his work as an SNY analyst since 2006.

But the emotional highlight is the exploration of his relationship with his 2 ½-years-older brother, Gary, who is interviewed in the film and played a key role in Hernandez’ development as a person and player.

“I wish that my parents could be alive for this, but unfortunately, they've been gone for a long time,” Hernandez said. “But my brother is very important to me. And he always has been and to this day, he’s still very important to me.

“We have a great relationship, a special relationship . . . He was like my talisman.”

During a question-and-answer session moderated by his SNY colleague, Gary Cohen, Hernandez marveled at his brother’s magnanimity as a college baseball star himself who did not resent his kid brother’s greater success.

“He was never jealous of me,” Hernandez said. “There are so many instances I can say where he was totally selfless. He could have been jealous of me. I know that. If the situation had been reversed and he had all the gifts, I would have probably been jealous. But not Gary. He's a special guy.”

Gary Hernandez is one of many interviewed in the film, including former teammates such as Dwight Gooden, Mookie Wilson and Darryl Strawberry, Jerry Seinfeld and even 90-year-old Whitey Herzog, whom Hernandez always has blamed for banishing him from St. Louis to the Mets in 1983. (Herzog blames ownership.)

When Cohen asked Hernandez to name his favorite part of the documentary, he said, “I think the comments from my teammates is what touched me best.”

Later, he asked Cohen for a tissue to wipe his tear-filled eyes.

With his number retirement drawing closer, Hernandez told Newsday, “I don’t think it’s going to really soak in until I step out on the field . . . It’s a great honor, what they're doing.

“What I love most, what I cherish most, is that only I'll be the sixth person (with a retired number) in 60 years of the Mets. So it's like one every decade, and I'll be the fourth player. It’s a select few, and that's something I'm really proud of.”