For Rob Reiner, 'Being Charlie' Is a Film That Brings Father and Son Together

— -- He's directed countless films, from comedies like "This Is Spinal Tap" to dramas like "A Few Good Men" -- but few have been as personal for Rob Reiner as his latest project, "Being Charlie."

That's because the film is co-written by none other than his son, Nick Reiner, who has penned a semi-autobiographical drama about addiction and the burdens of having a famous last name. The film's main character, 18-year-old Charlie Mills, having been in and out of rehab for three years, flees yet another program, renews a longstanding feud with his parents as his father makes a run for governor of California, and falls in love with a fellow patient.

For Nick, "Being Charlie" is the culmination of a long creative process that took nearly a year and started with a half-hour television comedy pilot. Having met co-writer Matt Elisofon in rehab, the two collaborated on a comedy about substance abuse and rehabilitation, which the elder Reiner suggested be turned into an hour-long drama-comedy. This then became a screenplay drawing on the experiences of the Reiners and others Elisofon and Nick had met in rehab.

Both father and son say that the filmmaking experience has helped them come to terms with a dark time in their own relationship -- Nick’s stints in rehab during his teenage years. "Over the course of making the film, our relationship definitely changed. It wasn't terrible or anything, but it got better, because I then understood a lot more of what he had gone through and he understood a bit more what I had gone through," Rob told ABC News.

For Nick, writing the character of Charlie's father meant coming to terms with his feelings about his own father during his battles with substance abuse. Written initially as a tough, harsh figure, Nick says he had to convince his father that it was not entirely a reflection of his own upbringing. “It was hard for him for a while to think that I thought of him that way, and to convince him that that’s not how I felt, but that fathers do get in that mode sometimes when they’re trying to help their kid,” he said.

Rob said that while collaborating with his son Nick was difficult and emotional at times, it was ultimately the most satisfying creative experience of his life. “[Nick] would challenge me and I have such respect for him because, as a young guy, with all the experience that I have, he was still able to challenge me and push me,” he said.

The end result is "Being Charlie," a deeply personal drama that means more to both of them than just another film. "Whether it's a piece of art or it's music or a film, you're investing yourself in the characters and portraying an extension of your thoughts and feeling. And so we're doing that, and so it turns out it became kind of cathartic," Rob said.

"Being Charlie" is out in theaters May 6.