Rob Reiner Spoke About Son Nick and the ‘Very Personal’ Movie They Made Together on TODAY in 2016

The acclaimed director’s most personal film was a 2015 movie with a screenplay co-written by his son, Nick, who has been arrested in connection with his death.

Rob Reiner was known for directing classic films like “When Harry Met Sally” and “The Princess Bride,” but his most personal film was released in 2015 with a screenplay co-written by one of Reiner’s sons.

The drama “Being Charlie” tells the story of an 18-year-old’s struggles with addiction, his time in rehab and his life in recovery. The film is based on the real-life experiences of Reiner’s son, Nick, 32, who was in and out of rehab facilities between the ages of 15 and 19 for drug addiction and lived on the street for periods of time.

Nick is one of three children shared by Reiner, 78, and his wife, Michele Singer Reiner, 65, who were found dead on Dec. 14 of apparent stab wounds at their Los Angeles home, a source close to the family told NBC News.

Nick has been arrested in connection with the deaths of his parents, two law enforcement sources with direct knowledge of the investigation told NBC News on Dec. 15.

Rob Reiner’s personal and professional lives became entwined in 2015 when he worked closely with Nick on “Being Charlie,” which he spoke about on TODAY in 2016.

“It was very personal,” he said about the film. “It’s not a secret, but my son Nick, who was one of the writers of the screenplay, had his problems with substance abuse. And he went through a number of rehab programs in the time he was 15 to 19. He’s doing very good now, but what I didn’t understand is the depth of what he was going through.”

The movie stars actor Nick Robinson as Charlie Mills, an 18-year-old son of a former Hollywood star running for governor of California. His experiences in rehab are depicted along with his life in a sober house and his romantic relationship with a woman also dealing with addiction issues.

The film also features “The Princess Bride” star Cary Elwes as Charlie’s father, as well as Common, “Homeland” actor Morgan Saylor and “Desperate Housewives” star Ricardo Chavira.

Nick Reiner co-wrote the screenplay with Matt Elisofon, a friend he met in rehab, and Rob Reiner directed the movie.

“The process of making this film not only forced me to see what (Nick) was experiencing, but I think it forced him to see what I went through and what is mother went through, and hopefully the film is a reflection of that,” Rob Reiner said.

The elder Reiner hoped that the movie would put a spotlight on the issue of drug addiction in the U.S., which was particularly salient in 2016 amid a crisis of deaths from opioid abuse.

“Clearly there’s no socioeconomic boundary to this,” Reiner said. “This is touches everyone. The disease is not the addiction. The disease is the underlying issues that cause you to self-medicate with either alcohol or drugs or gambling, sex, whatever it is you do. That’s an individual thing and that has to be treated individually. I don’t think it works in kind of a cookie-cutter kind of approach.”

Reiner said his son hit it off with Elisofon in rehab after watching Elisofon perform a standup comedy routine.

“And then when they got out, they started writing,” Reiner said. “At first it was like just a half-hour comedy of life in rehab. And they showed it to me, and I said, ‘You know, it’s funny, but it goes a little deeper than this, and I think if you’re going to do justice to it, you got to bring the emotional part of it out,’ and eventually it became this screenplay that we worked on.”

Reiner called for compassion for those facing addiction issues.

“We have to not punish people who have problems,” he said. “We have to help them, and I think we’re going in that direction now.”

The Reiners shared son Jake and daughter Romy along with Nick. All three were at the September premiere for “Spinal Tap II: The End Continues” in Los Angeles in support of Rob Reiner. The late director was also the father of daughter, Tracy, 61, whom he adopted while with his ex-wife, the late director Penny Marshall.