Brian Wilson: Long Promised Road explores fame, failure and the Beach Boys' lasting legacy, as Danielle de Wolfe discovers from director Brent Wilson.

As the age old saying goes, you should never meet your heroes. In the case of director Brent Wilson, it's a warning he chose to disregard entirely, instead charging headfirst into the California sunshine and a world inhabited by one of surf rock's founding fathers.

Sharing a surname but no relationship, the Bon Jovi: Inside Out documentarian saw the spheres of work and play seamlessly converge when it came to Beach Boys founding member Brian Wilson. A life immortalised as part of the new feature-length documentary Brian Wilson: Long Promised Road, the project is, in the words of both Wilsons, quite literally "a trip".

Created with the help of Brian's long-time friend and former Rolling Stone editor Jason Fine, the project is one of enlightening extremes. Exploring the soaring highs of the band's chart-topping success, alongside the altogether darker lows of the musician's well-documented drug abuse and mental health struggles, the candid conversations that emerge as Fine and Wilson road-trips through California offer a snapshot into a remarkable mind.

"Brian is incredibly intuitive; he really does pick up on people's vibrations," reflects Brent with a brief nod. "When you speak with him, he'll look just a little bit above your head. And a lot of people told me - people that have known him for a long time - that he's literally probably looking at your aura."

It was a concept born on a warm June evening from the fifth row of the Greek Theatre in Los Angeles. A show that marked the musician's 75th birthday, Brent recalls how the audience's adoration for the Beach Boys' founding member, alongside the visible respect shown by his family and fellow musicians, left the director questioning "how on earth did Brian Wilson get here?".

"For me, it's just as much a film about friendship, I think, as it is about anything else," says Brent. "Jason and I agreed on really early on - we kind of took a Hippocratic oath with this, which was 'do no harm'. And if Jason asked Brian a question, and he didn't want to talk about it, we just wouldn't go there."

Standing as testament to Wilson and Fine's close-knit relationship, the documentary's emotional dashcam footage conveys a tender friendship forged over the course of several decades. Describing how Fine "made the mistake" of offering to "do anything" in order to assist with the project, the director admits that without the journalist's help he would have been unable to capture the "intimacy" required for such a film - an insight "Brian's fans deserve".

Starring a host of world-renowned names, the film also features anecdotal tales and insights from a range of musical contemporaries, including Sir Elton John, Bruce Springsteen and Nick Jonas.

"I tried to interview Brian initially - as you'll see in the beginning of the film - and like every other interviewer of Brian Wilson, it doesn't end well. He doesn't like to be interviewed. I knew I was failing miserably and my movie was probably going to fail miserably if I didn't try to do something."

Renowned for being a man of few words, Brian's linguistic skills instead came into their own when paired with the syncopated rhythms of hits including Surfing USA, I Get Around and Wouldn't It Be Nice. A nine-time Grammy Award nominee, two-time winner and Rock and Roll Hall of Fame inductee, Brian's expansive list of musical accolades is downright enviable. It makes sense then, that the biggest challenge posed by such a project centred around incentivising a 79-year-old who wants for very little.

"It's hard to speculate, but I think Brian maybe saw this film - because he agreed to do the film really easily - as an opportunity to say some things that he hasn't said, particularly with his brothers," says Brent pensively. "That was something I was really surprised by and I didn't expect, because I knew that was going to be painful for him."

Comprised of the three Wilson brothers - Brian, Dennis and Carl - alongside cousin Mike Love and friend Al Jardine, the Beach Boys' original line-up was short lived following the untimely death of Dennis, who drowned in 1983. Not long after, Brian found himself estranged from the group, with his youngest brother Carl dying from lung cancer in 1998.

"Brian is the last Wilson," reflects Brent, noting the inevitable pain that comes as a result of an eldest child losing all their younger siblings. "I know how much he loved his brothers and how complicated their relationships were, so I didn't expect him to talk that much about them. When he started to discuss those, for me that was a lovely surprise. It's shaped the film, to be honest with you."

For the musically inclined, this dark sense of melancholy can be heard drifting through even the most upbeat Brian Wilson-penned tracks. It's a sound Brent describes as "loneliness" and "almost a cry for help" - a notion that becomes increasingly apparent when contextualised against a life shaped by abuse, loss and creative isolation.

"Wouldn't It Be Nice, to me, was a question mark," explains Brent, half lost in thought. "There was always this kind of little undercurrent - if you're open to that, and I think like so many serious Brian Wilson fans, it was that undercurrent that pulled me in."

Describing the Beach Boys' track In My Room as "the gateway drug" that led him to discover artists such as Bruce Springsteen and Jim James, Brent notes the way in which his own musical education was shaped by the band's ground-breaking harmonies and distinctive "textures".

"As crazy as it may sound - and it sounds kind of silly just hearing in my head, but I literally thought to myself, 'What if there was 70 hours of interviews with Beethoven or Mozart or Hemingway? How valuable would that be intrinsically to the world 100 years from now?' And that's the way I approached it," says Brent.

"I really, truly want this to be a film that lasts the ages and gives [an] insight into Brian that people haven't seen before."

Brian Wilson: Long Promised Road is in cinemas now