Natalie Wood's Daughter Defends Her Father Robert Wagner: 'He Would Have Given His Life for Her'

It’s taken over three decades for Natalie Wood‘s daughter, Natasha Gregson Wagner, to tell the story of her mother, who died by drowning on Nov. 29, 1981.

Now 49, Natasha is ready to share who her “brave and strong” mother truly was in a new documentary Natalie Wood: What Remains Behind, (premiering May 5 on HBO) and in her memoir More Than Love, excerpted exclusively in the next issue of PEOPLE.

So devastating was the loss for Natasha, who was then 11 years old, that for many years she blocked out the details of her mother’s death. It was too painful to think about how she ended up alone in the waters off of Catalina Island after a weekend spent on their yacht, the Splendor, along with her husband Robert Wagner, and actor Christopher Walken, with whom Wood was making a movie.

But the question fueled years of painful tabloid speculation that Wagner, the man who raised Natasha and her stepsisters Katie and Courtney Wagner, had failed to save his 43-year-old wife. Stories which often eclipsed the life and work of the soulful actress, who starred in such classic films as West Side Story, Gypsy and Rebel Without a Cause. (Natasha’s biological father Richard Gregson and Wagner agreed that it was best for Natasha to stay with her stepfather after her mother’s death so all three sisters could be raised together.)

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“It’s outrageous and completely unacceptable that others have created this narrative about my dad and the night my mom died,” says Natasha. “I know that if my mom had been in any kind of distress he would have given his life for her. I know that as as well as I know my name.”

Wood’s death was ruled an accidental drowning and believed to have happened after Wood slipped overboard while intoxicated. (The case was reopened in 2011. Two months later, a sheriff’s department official told the Los Angeles Times that detectives found no new evidence to dispute the official findings.)

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Now for the first time, Natasha examines what happened that night, and in the film, asks her father about that fateful weekend.

Fighting back tears, Wagner describes the moment he got the news that his wife’s body had been found. “Everything went out from under me,” he tells her. “That night has gone through my mind many times.”

“You could hear a pin drop,” says the film’s director Laurent Bouzereau. “We decided to leave it as raw as possible. We wanted the moment to feel the same as I felt when filming it. You feel the pain of the tragedy in a deep deep way.”

For more on Natasha Gregson Wagner and her mother Natalie Wood, pick up this week’s issue of PEOPLE, on stands Friday.

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The documentary also features many never-before-seen home movies and photographs, reminders of a life tragically cut short.

Now married to actor Barry Watson and a mom to their 7-year-old daughter Clover, Natasha hopes the film and her book will remind people of the dazzling, deep and complicated woman who loved her family.

“Sharing my experience of grief and trauma and heartbreak and deep sadness, maybe connects us to others who have felt that way. In the shared retelling, there is healing,” says Natasha. “I know she wanted me to write the book and she wanted the documentary to be made, and this is how she wants to be remembered.”

Natalie Wood: What Remains Behind will premiere Tuesday, May 5 at 9 p.m. ET/PT, exclusively on HBO.