Christopher Reeve's Son Reveals the Last Time He Saw His Father 'on His Feet' in New “Super/Man ”Documentary

'Super/Man: The Christopher Reeve Story' premiered in January at the Sundance Film Festival and will appear in theaters in September

Christopher Reeve's real-life story of tragedy and triumph is coming to the big screen.

On Monday, August 26, DC Studios released the first trailer for Super/Man: The Christopher Reeve Story, a new documentary that had its world premiere at the Sundance Film Festival back in January.

The movie is emotional journey that portrays the late actor and his family’s unwavering support after a 1995 equestrian accident left him paralyzed. The star died in 2004 at age 52.

"We said goodbye, he gave this wave," Reeve's son Matthew recalls in a clip previously released from the film, describing his final exchange with his father before the accident. "That was the last time I saw him on his feet."

Super/Man includes intimate interviews with Reeve’s three children Matthew, Alexandra and Will, as well as his late wife Dana, who died in 2006 from lung cancer. It also features memories from Reeve’s friends including Whoopi Goldberg, Susan Sarandon, Jeff Daniels and Glenn Close.

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Related: Christopher Reeve's Son Recalls Dad's 'Incredible' Oscars Appearance After Paralyzing Accident (Exclusive)

Reeve's children attended the Super/Man screening held at the Ray Theatre in Park City, Utah, during Sundance. In the film, they give candid, emotional interviews about their family’s life, once led by their heroic father and caregiver mother.

"This year, in October, will be the 20th anniversary of dad's passing," Matthew, 44, said during a Q+A after the screening of why it felt like the right time to make the film.

He went on to say that he and his siblings had been approached with "a few inquiries" over the years, but entrusting his family's story to this specific team, including filmmakers Ian Bonhôte and Peter Ettedgui, just felt right.

"It all came together really organically," Matthew added.

Related: Inside Christopher Reeve's Early Days as a Theater Actor in N.Y.C.: He 'Definitely' Had Star Power (Exclusive)

Speaking exclusively to PEOPLE in March, Jane Seymour opened up about Reeve, who was her close friend and costar in the 1980 movie Somewhere in Time.

"He was just an amazing guy. He was really bright, he was fearless and he loved to be alone. He loved to fly airplanes and sailboats and ride horses," said the actress, 73.

Seymour also opened up about the things she's "excited about the public" getting to know Reeve in the documentary, and praised his activism.

"He took all his energy and all his intellect and all his visibility to really move the dial and get the stem-cell thing going when nobody wanted to do that. Now it's normal," she said.

Super/Man: The Christopher Reeve Story is in select theaters on Sept. 21, with an "Encore Presentation" on Sept. 25, Reeve's birthday.

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