Eric Clapton has lived a life of extreme highs and devastating lows, so it's understandable that he might find the new documentary Eric Clapton: Life in 12 Bars difficult to watch.

When asked Monday about whether any of the film's footage of his younger self embarrassed him, the guitar legend was blunt.

"The whole thing. Are you kidding? The whole thing…right up to the time I stopped drinking, everything I said [was] absolute blather," he told reporters at a TIFF press conference Monday morning, after the doc's Sunday evening world premiere in Toronto.

Eric Clapton on watching his pompous younger self1:05

"There's a certain amount of pompousness that I see when [I was] being interviewed," noted the virtuoso from bands such as The Yardbirds, Cream, Blind Faith and Derek and the Dominos. 

"Maybe it's true for all of us when we're young: there's a level of arrogance there that 'I know it all.' Only as I get older do I realize that I know nothing at all, whatsoever."

Still, Clapton gave filmmaker Lili Fini Zanuck, the Oscar-winning producer behind movies like Driving Miss Daisy, Cocoon and Mulholland Falls, complete licence to fully explore his life story and approached her with the idea of what would become her first documentary as a director.

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Director Lili Fini Zanuck and musician Eric Clapton, seen promoting the documentary Eric Clapton: Life In 12 Bars" in Toronto Monday, first worked together when she asked him to score the 1991 crime drama Rush. (Kevin Winter/Getty Images)

"I was somewhat concerned that there may be an impression because we'd been friends for so long that I would whitewash something or Eric would say take it out," said Fini Zanuck, who had first worked with Clapton on her 1991 crime drama Rush.

"None of that happened because of the trust that we have and the fact that he gave me the responsibility and didn't second guess me."

The revealing portrait — told through voiceover from Clapton himself, as well as interview excerpts from family, friends, collaborators, and heroes like B.B. King, Duane Allman, Jimi Hendrix, George Harrison and Pattie Boyd — doesn't flinch about some of the musician's darkest moments: a traumatic relationship with his birth mother, decades-long substance abuse battle, tumultuous love life and the heartbreaking accidental death of his young son, Conor.

However, again and again, "Music saved me,"  Clapton says in the film, which taps into a wealth of archival photos, videos, audio interviews, recording sessions and even his own childhood drawings and paintings to tell the story of how a nine-year-old Blues fan became a generation-defining music icon.

"This wasn't a period of time when people whipped out a phone and said 'Let me have a picture taken with you,'" Fini Zanuck noted, saying she felt lucky with many archival finds, from home video footage of Clapton's youth that came from a family member who just happened to have kept it, to unearthing a rare radio interview of Allman talking of his time jamming with Clapton in Derek and the Dominos.

"Things like that, those are real treasures," she said.

Eric Clapton: Life in 12 Bars will air on Showtime on Feb. 10, 2018. A theatrical release is also expected.

The Toronto International Film Festival continues through Sept. 17.