It's a wince-inducing moment I won't ever ever forget. I am sitting in a swanky London hotel suite with Prince and he is asking me for the title of a book I once wrote about him.
For a second I consider lying outright, telling him the book was called Prince: The Biography - or even Prince: A Pop Life, the title of a rival biography that came out shortly after mine. But eventually he drags it out of me.
"It was called Imp of the Perverse," I say, bracing myself for an unholy hissy fit.
"'Imp', huh," he says menacingly. "That's what, a small person?"
"More a sprite, a mischievous creature," I plead.
"What about 'Perverse'? Same thing as perverted, right?"
"I meant it more in terms of, you know, deviating from the norm."
"And what gave you the right to write a book of conjecture about my life?"
"What gave me the right? How about, it's a free country?"
"Did you come to the source for the truth?"
"Did I what?"
"Did you come to the source for the truth?"
"You think I didn't try to get an interview?"
Actually, I'd been trying to get an interview with Prince for almost 20 years, ever since seeing him live in New York City in the spring of 1981. I thought he was the most exciting American pop star of the 1980s, a protean genius who straddled every musical genre from funk to heavy metal; who danced like a souped-up Nijinksy, played guitar like a demon, and sang like an androgynous angel.
Of the four major stars of that decade - Madonna, Michael Jackson and Bruce Springsteen were the others - Prince was the one true maverick. And the more successful he got, the more mysterious he became. By the time I tagged along for part of his 1999 US tour in 1983, he had ceased speaking to the press altogether. At the show in Kalamazoo, Michigan, I was brought to his dressing room to shake his hand; that was the beginning and end of any direct contact with a man the media had dubbed His Royal Purpleness.
"Why do you have to know who I am?" Prince had asked interviewers as early as 1979, when, for a brief instant he could have been any post-disco R&B singer. Five years later, on the 12-million-selling Purple Rain, he sang that: "I am not a woman, I am not a man/I am something that you'll never understand."
"In some respects, Prince was an all-American boy," his former engineer, Susan Rogers, later told me. "But there was some abuse in his childhood and he had a weird name [his parents named him Prince Rogers Nelson] and he was smaller than his classmates."
It wasn't easy to be young, gifted and black in Minneapolis-St Paul in the mid-1970s. In the Twin Cities, where African-Americans accounted for a mere three per cent of the population, white rock was the staple musical diet of Prince and his pals. The trail that Jimi Hendrix and Sly Stone had blazed in the late 1960s - marrying rock to R&B - was the musical path that Prince took.
Warner Brothers swiftly saw that he was the genuine article, a wunderkind who had already synthesised his own style. When he demanded the right to produce his own debut album, Warner gave him the green light. In 1979 he scored his first hit, the insatiably funky - and already mildly risqué - I Wanna Be Your Lover.
Just as Prince looked set for mainstream R&B success he threw a curveball, reinventing himself as the lewd "punk-funker" of 1980's Dirty Mind. The album was a critic's dream: a black kid from the Midwest breaking all the demographic rules, as much new-wave rocker as soul loverboy. To my mind it remains Prince's best, a lo-fi mix of gritty guitar and cheap keyboards. Most of Prince's peak moments - When Doves Cry, Kiss, Sign O' the Times - stem directly from this minimalism.
Rather unsubtly, he titled the next album Controversy. The scandalous edge was essential to distinguish himself from mainstream rivals such as Michael Jackson. Prince's persona made it clear he was offering himself as a kind of lewd Rolling Stones to Jackson's boy-next-door Beatles.
With Little Red Corvette, however, he plugged directly into the new world of MTV, crossing over to white America. He even created an ersatz Minneapolis "scene" by assembling acts such as The Time and Vanity Six. The whole strategy climaxed in the multi-media phenomenon that was 1984's Purple Rain.
The drive to succeed was relentless. For Rogers, Prince was a workaholic slave-driver whose obsessive productivity masked a deep, inner emptiness. "It was compulsion, it was ambition, but it also filled a vacancy in his life," she told me. "We'd spend time talking but it was always while working."
The vast Paisley Park complex outside Minneapolis became a private Xanadu, where Prince could exert total control over his career. "He constructed a universe where nothing touched him," said Alan Light, the then editor-in-chief of Vibe magazine. "If he didn't choose to come out of that music bubble, he didn't have to."
Like many a pop genius, from Phil Spector to Morrissey, Prince's people skills left much to be desired. "He can be charming, but he can equally be utterly loathsome," Chris Poole, his former UK press officer, told me. "It's almost like this incubus figure appears in front of you."
When Oprah Winfrey visited Paisley Park in late 1996, Prince slyly alluded to the fact that therapy had revealed the presence of an alternate personality. "I absolutely concur with him that there may be more than one in there," his former manager Owen Husney told me. "One was a more nurturing personality, the other was the more hurt side. If you're a control freak like him, you're just trying to control your environment so you won't get hurt.
Then again, the whole thing might just have been an act. "Maybe I appeared to be shy," he told me three years later in that swanky hotel suite. "But appeared is the key word there. I've only really ever given you music. I'd give cryptic little answers to questions that made no sense. I've always really been the same person."
Prince's run of 1980s albums dripped with invention, experimentation, emotion - and, of course, raunchy. His live shows were non-stop parades of narcissistic exhibitionism that referenced Little Richard, James Brown and P-Funk. For most critics and many fans he reached his creative peak with the dazzlingly eclectic Sign 'O' the Times (1987).
The 1990s, on the other hand, was a frustrating decade of mostly shoddy music and undignified conflicts with record companies. When Prince daubed the grotesque word "SLAVE" on his cheek to protest the terms of his deal with Warner Brothers, Owen Husney saw it as "slashing the faces of those who'd protected him". The dry funk-gospel of Kiss and twisted weirdness of If I Was Your Girlfriend were gone. Though he continued to pack out arenas all over the world, creatively Prince had been left stranded by the very R&B and hip-hop artists he had influenced.
Of course, there is a smattering of great music from the past 20 years; the writer Matt Thorne recently sent me a compilation of Prince tracks from such little-known albums as New Power Soul (1998) and Lotusflow3r (2009) that proved as much. Even this year's 20Ten has its moments. But most of Prince's latterday work sounds like it has been made on autopilot, and he must know it.
Does he have any more significant music left in him? I think he should go back to the Dirty Mind drawing board and write 10 raw, emotional songs about where he is at in his life. Only then will he reconnect with the world at large and become relevant again.
Four years ago I watched Prince perform at his Beverly Hills mansion as part of an evening designed to promote the underwhelming 3121 album. Although he was essentially backing Tamar - one of the countless protégés he has nurtured to little or no effect over the decades - the man's charisma was undiminished.
After the evening was over, I walked out into the balmy LA night and asked myself if he actually cared about being a superstar again. Did he genuinely want to compete with the Jay-Zs and Kanye Wests, or was he just content to preach to the converted faithful?
"A strong spirit transcends rules," he'd told me in 1999. "As RZA of Wu Tang said: 'I ain't commercial, it's y'all who tell me whether I'm commercial or not'."
Barney Hoskyns is the co-founder of Rock's Backpages [www.rocksbackpages.com], the online library of more than 17,000 seminal interviews and reviews from the music press of the past 40 years. His latest book is Lowside of the Road: A Life of Tom Waits (Faber).