The weird world of Joaquin Phoenix

He went from Oscar nominee to bearded crackpot bent on a rap career. But the 'meltdown' was all an act, writes David Usborne

When Joaquin Phoenix appears on the Late Show with David Letterman next Wednesday, he will not be in a caveman beard and will attempt coherent conversation. Or so we are told. In other words, when it is over, Letterman will not have to repeat what he said the last time the actor was on: "I'm sorry you couldn't be here tonight."

Those were distressing hours for fans of Phoenix, who last mesmerised us as Johnny Cash in the 2005 biopic, Walk The Line. The unkempt, bloated and altogether unprepossessing man on the Letterman couch in February last year was nothing like the witty, gloweringly handsome talent we thought we knew. What had gone wrong?

Nothing had gone wrong, or plenty had. It depends on who you talk to. Phoenix, whose brother, River, died of an overdose outside Johnny Depp's Viper Room in Los Angeles in 1993, had not been pushed into tragic mental implosion by the pressures (or vacuous inanities) of stardom. We didn't know it then – and nor did Letterman – but he was merely staying in character for a fictional film about a famous person – him – suffering such an implosion, thumbing his nose at those inanities and plunging instead into a rowdy hip-hop career.

We learned this during the past week, courtesy of Casey Affleck – his friend of 20 years and his brother-in-law. Affleck directed the film in question whose title, I'm Still Here, is inspired by the Letterman quip. It opened in the US last week to mostly searing reviews. The veteran critic Roger Ebert called it "a sad and painful documentary that serves little useful purpose other than to pound another nail into the coffin" of a once-blossoming career.

It may have been reactions like that – and the film making barely $100,000 (£65,000) in a limited release in the US last weekend – that prompted Affleck (brother of Ben) to step forward and admit in an interview with the New York Times that nothing in it is real. While it purports to document Phoenix jumping the celebrity rails and opting instead for a life of cocaine, whores and degrading racist language (and hip-hop), actually it was all staged.

Now what to think? The film turns out to be, at best, an inspired piece of performance art instigated so thoroughly that it went on for two years without any of us realising it. At worst, it was a pathetically self-indulgent wallow by members of two of the most talented families in Hollywood, who should have known better and done something useful during all those months. We might feel entitled to feel duped. The degree of deception was quite elaborate. The opening scene that shows the Phoenix children diving into a pond in Panama in 1981 before an applauding father was actually filmed with actors in Hawaii. To achieve the grainy quality, Affleck made his print on an old video cassette that already had the film Paris, Texas recorded on it.

It even seems that Phoenix's agent with the William Morris Agency was persuaded to go along with the two-year charade. More than that, he actually took a small part in the film. Affleck said that no one need feel affronted. "The reviews were so angry," he said. "I never intended to trick anybody. The idea of a 'hoax' never entered my mind." He added that for the film, Phoenix turns in what is surely "the performance of his career".

Danny Perkins, managing director of Optimum, the film's UK distributor, said it doesn't make a difference whether the film is staged or not. "Beyond all the hype and the hoopla that the film is about, it is actually a moving film. If it is a performance, it is an incredible performance. To me, it feels like it started out as a joke and it got bigger and bigger." He added that Optimum is "fine" with the film and that he doesn't feel hood-winked. "It stands up as a film. We're happy with it."

Even now, not every critic is certain that the breakdown portrayed by Phoenix was not real, whatever Affleck is now claiming. At one point in the film, when the beard is established and all the normal Hollywood rhythms have been abandoned, Phoenix declares that he's sick of "a self-imposed prison of fucking characterisation. I don't want to play the character of Joaquin anymore". He wails about feeling "fraudulent" as an actor and how he has had enough of being "just a fucking puppet".

"This, I think, is no put-on," insisted Jeff Simon of the Buffalo News. "What you're watching seems to me pure breakdown. I don't know if the old-fashioned phrase 'nervous breakdown' is apt, but this, for 108 minutes, is assuredly spiritual, moral or emotional breakdown – something."

In a story with much irony to go around, it is worth observing that many more people will have seen the Letterman clips than are likely to see the film itself. The audience for his return to the Late Show on Wednesday may be even larger. Then we might be able to make a more reasoned assessment of whether the old Joaquin Phoenix is still with us – and getting ready to star in new films again.