In the autumn of 1970, Eric Clapton summoned a young woman called Pattie Boyd, one of the leading British models of her generation, to the South Kensington flat used by his band.
There he produced a cassette tape of a recently completed song and played it three times, studying her face carefully for a reaction.
Blonde-haired, blue-eyed and breathtakingly beautiful, Pattie was already spoken for, married to his best friend and fellow musician George Harrison, reports Daily Mail.
Yet Eric was hopelessly infatuated and this music, with its lovelorn, wailing guitar and pleading lyrics had been composed in adoration – a shameless attempt to woo her.
The song was Layla, and its effect was overwhelming. Listening to it provoked awe that "the most powerful, moving song I had ever heard" should have been written about her, Pattie now recalls, although she was concerned that it would be instantly decoded, not only by her husband, family and friends but by the tens of thousands of strangers who would buy the album it featured on.
But, she says: "The song got the better of me. I could resist no longer."
And so, step by step, Pattie surrendered, caught between the rival attentions of Eric and George in music's best-known love triangle.
She also became the rock world's most famous muse, not only the inspiration for Layla but for Clapton's other great hit, Wonderful Tonight, and Harrison's Something.
The reality of life with Eric was something else, however. After kicking a heroin habit, he became a desperate alcoholic and, from his 20s to his 40s, a womaniser on the scale of Mick Jagger, a sex addict before the term was invented, with a jaw-dropping recklessness all his own.
"He never had to do anything," observes one source who knew him in the 1980s. 'Women just stuck to him like iron filings to a magnet.'
For those women, the price of his infatuations could include addictions as bad as his – or worse – and lives permanently scarred. Clapton, meanwhile, moved on without a backward glance.
It had been two years earlier that Eric first met 24-year-old Pattie, after a performance by his band Cream at the Saville Theatre in London. The musician thought her the most beautiful woman he'd ever seen and assumed her to be immeasurably above and beyond him.
"She belonged to a powerful man [Harrison] who seemed to have everything I wanted," he recalled. "Amazing cars, an incredible career and a beautiful wife… they were like Camelot. I was Lancelot."
He could only watch as the Harrisons' marriage staled, reflecting how different he would be in George's place, but reduced to admiring Pattie's clothes or praising her cooking when he went for meals at their house.
After more than two years together, Pattie had come to terms with George's coldness, the obsession with meditation that often made her feel invisible to him, the infidelities he no longer tried to hide.
Yet she remained oblivious to Eric's interest in her. She was hardly the only woman Clapton was chasing, after all. Both George and Eric led love lives of bewildering complexity.
In September 1969, despite his feelings for Pattie, Eric became engaged to Alice Ormsby-Gore, youngest daughter of the 5th Baron Harlech, a former Conservative government Minister and British Ambassador in Washington. George, meanwhile, was showing more than a brother-in-law's interest in Pattie's younger sister Paula.
The Beatle decided to seduce Paula, but needed to get Pattie out of the way first, so in late 1969 he suggested Eric take her out for the night to keep her occupied.
However, the plan misfired – and it was not George but Eric who ended up with Paula, apparently unable to resist because of her resemblance to Pattie. Such behaviour by rock megastars was tolerated, even expected, in a climate barely affected by feminism.
"They'd been famous from a youngish age without growing up first and having any experience of normal life," says Pattie. "They'd had too many toys too quickly… they thought they could do whatever they wanted."
The following spring, in March 1970, a letter marked "Express" and "Urgent" arrived at Friar Park, the fantastical Gothic stately home near Henley that Pattie shared with George. It said: "what i want to know is if you still love your husband or if you have another lover? if there is still a feeling in your heart for me… you must let me know! all my love."
That evening, Eric rang, asking, "Did you get my letter?" Pattie replied that its contents had come as a total shock and the call ended in embarrassment and confusion. From then on, however, Pattie and Eric began a flirtation.
At first she saw it as a way of paying George back, mildly and in secret, for his infidelities and coldness. She was unwilling to endanger the marriage – and cheating on George with his best friend was unthinkable.
There was another powerful reason for keeping her feelings for Eric firmly under control: he was having an affair with her sister Paula, even though he was living with and engaged to Alice.
Friar Park was only 90 minutes by road from Clapton's Italianate Surrey mansion, Hurtwood Edge, and Eric frequently dropped by during George's many absences, albeit for no more than a chaste glass of wine or cup of tea.
Further secret assignations took place in Guildford, the two meeting under the town clock like characters in a flare-trousered version of Brief Encounter. But Eric's frustration at the situation was intensifying.
Such was the extremity of his obsession, he even sought help from the supernatural in the form of a white blues singer and pianist called Dr John, a sinister-looking figure who performed in the Mardi Gras costumes of his native New Orleans and was said to have voodoo powers.
Eric went to Dr John in June 1970, explained the Pattie situation and requested a "love potion number 9", like the one in the Coasters song, that would make her leave George for him.
The supposed witch doctor gave him a small box of woven straw to carry in his pocket and written instructions for a ritual that would cast the necessary spell.
Eric, who believed totally in the charm, "did exactly as I was told".
The powers of darkness were not given much time to act. Eric and Pattie both attended the first night of the musical Oh! Calcutta! a couple of weeks later.
George opted to stay away, then, gripped by a pang of possessiveness, spontaneously drove to the aftershow party. There he found Pattie in the garden with Eric. "He asked what was going on," Pattie recalls, "and to my horror, Eric said, 'I have to tell you, man, that I'm I love with your wife.'"
George made no response – probably because it was no real surprise – but merely asked her which of them she would be ending the night with. Resisting whatever Voodoo power might be emanating from Dr John's straw box, Pattie replied firmly, "I'm coming home with you, George."
Eric would not be deterred and that autumn, not long after he had played the tape of Layla, he turned up unexpectedly at Friar Park while Pattie was alone. Now he told George's wife he couldn't live without her and that she had to come away with him this very minute.
When she refused, he took a small packet from his pocket and said it contained heroin, which he'd take if she didn't do as he asked. Horrified, she tried to grab the packet, but he held it in his clenched hand.
He said "Right, that's it, I'm off", and left, presumably to plunge into a deadly habit for which Pattie would carry the blame.
This was emotional blackmail of a shameless kind. What Pattie did not know – but which would soon become all too apparent – was that Eric was already in the grip of heroin addiction and had been for months. Heroin brought a sensation of total calm, self-confidence and comfort inside one's own skin that Eric had never really felt in his 25 years.
Bobby Whitlock – a bandmate in Derek and the Dominos, the shortlived group that recorded Layla – remembers Eric taking heroin in the cafeteria at Abbey Road studios during recording sessions, something The Beatles would never have dared.
The Layla album sessions in Miami had been saturated in drugs, including heroin, but the collapse of Derek and the Dominos in 1971, allied to the continued impasse with Pattie, marked Eric's descent from occasional heroin-user to addict, snorting the drug using a gold spoon he wore round his neck.
Outwardly, Eric and Alice appeared to be an enviably cool couple, spanning the class divide with charm. But when their supplies of drugs ran out they'd go berserk, banging their heads against walls or burning themselves with cigarettes.
The next three years of what should have been the best time in Clapton's life were not just ruled by heroin but lost to it. It obliterated his creativity and took away the work ethic that had driven him from the first moment he picked up a guitar.
He sought no new musical partners, wrote no new material, and released no new records; just stayed holed up at Hurtwood Edge, semi-comatose.
The cost of the heroin was running at £1,000 a week, equal to £10,000 today. Alice would never recover from her addiction, dying from a heroin overdose in 1995.
Arthur Eggby, Eric's gardener and handyman, became accustomed to the sight of Eric laying out four lines on the kitchen counter and inhaling them through a tightly-rolled £50 note that he would then toss into the waste-bin.
Since the notes had officially been thrown away, Eggby felt justified in covertly retrieving them, sponging off the heroin and hanging them up to dry in the kitchen for his next holiday on the Isle of Wight.
At the invitation of their friend and fellow rocker Pete Townshend, Eric and Alice went to see The Who perform in Paris, taking enough heroin to last the day but obliged to get home by midnight, like two smackhead Cinderellas.
Eric's drug-addled purgatory continued until August 1973 when Alice's father Lord Harlech wrote to Eric with an ultimatum: kick heroin or he'd turn him, and his daughter, over to the police.
Eric agreed to live with Dr Meg Patterson, a Scottish neurosurgeon who claimed to be able to reduce heroin withdrawal symptoms by a treatment of her own invention called Neuroelectric Therapy, a form of acupuncture. It worked.
The second stage of his recuperation involved staying on the Harlech family's farm near Oswestry in Shropshire where the rock star mucked out animals, dug ditches and baled hay.
It was not until 1974, when Eric was on his comeback tour in the US, that the news arrived: Pattie had finally left George.
Since Eric had revealed his obsession, George's swings from Hindu spirituality to coke-fuelled promiscuity had become more blatant, even having sex with Ringo Starr's wife, Maureen, at Friar Park while Pattie was actually in the house. It was too much.
Clapton was told Pattie was in Los Angeles, staying with her other sister Jenny, who had married Mick Fleetwood of Fleetwood Mac.
Eric called her, inviting her to meet him in Boston on July 12 when he was due to perform, and this time, she said yes.
Her long resistance to Eric had melted into 'an intoxicating, overpowering passion' utterly different from the 'deep, gentle love' she'd felt for George.
Unfortunately, with Eric the reverse happened: the obsession he had nurtured at a distance for five years began to ebb away the moment he won her.
Pattie joined the tour briefly but after she'd left, Eric continued to sleep with other women as if nothing had changed.
Pattie's future was settled as she, Eric and George sat together in the hall at Hurtwood Edge – although she might as well not have been there. "I suppose I'd better divorce her," George said.
"Well, if you do divorce her," Eric replied, "I suppose that means I've got to marry her."
There was no trace of awkwardness between the three of them.
George turned up at Hurtwood on Christmas Day that year, scolded Pattie for abandoning vegetarianism and accepted some wine and Christmas pudding.
"I was caught in the middle between these two incredibly manipulative men, feeling as if I'd become invisible," Pattie said later.
By the late 1970s, Eric had moved seamlessly from heroin addiction to the alcoholism that would come to rule his life just as powerfully, and for much longer. While heroin had kept him generally docile, alcohol made him touchy and aggressive and prone to picking fights in public.
His tipple of choice was Courvoisier brandy, diluted with 7Up.
He would start soon after breakfast and work through two bottles a day. After 4pm, his manager, Roger Forrester, would substitute the brandy with cold milk-less tea to sober him up for the stage, usually without Eric noticing the difference. At night, he took a pint of brandy and 7Up to bed with him.
Alcoholism made Eric difficult and unpredictable, refusing to touch the food Pattie had spent hours cooking, bursting into rages and, once, crashing his Ferrari on the 300-yard return journey from the pub. His drunken pranks could be dangerous. Eric's devotion to West Bromwich Albion involved a trip by train to see them play Manchester City, where they won 1-0.
Nigel Carroll, Eric's personal assistant, recalls: 'On the way to the station, we passed a model shop and Eric went in and bought a replica handgun.
"We're sitting on the train when a Manchester supporter comes through the first class section and says, 'You had a lucky win today.' Eric takes out the replica gun, puts it on the table, and goes, 'This says it wasn't.'"
One night in Honolulu, hotel staff spotted him climbing from his 30th-floor room into an adjoining one, clad only in pyjama bottoms and carrying a Japanese Samurai sword – at horrific risk to his genitalia.
The idea was to give a passion-killing surprise to his drummer, Jamie Oldaker, who was in bed with a girl.
She began to scream hysterically and two security guards instantly materialised, pointing handguns at the marauding Clapton.
Pattie was no longer going on tour, but was in no doubt about what Eric got up to, for the evidence had a way of turning up at Hurtwood.
One winter day she answered the door to a young Spanish woman in torn jeans, to whom Eric had given his address.
Yet Pattie recalls moments of huge affection. "He could be so funny. When I was cooking, he'd make me put all the kitchen gadgets like the blender on at different speeds and then write music from the noise they made together.
"When he was too drunk to drive and I insisted on doing it, he'd simply move over and sit on my lap."
But his chronic addiction was taking its toll on Pattie, too. She now lived with a drinker who attended AA meetings but at the same time hid alcohol all over the house or in his cars.
Pattie wanted a baby but failed to conceive and turned to IVF, but one attempt after another failed and, in September 1984 – with her fertility treatment still continuing – she walked out on Eric, choosing a moment while he was comatose on the sitting-room couch.
It was the beginning of the end for one of the greatest rock romances, a disintegration which would throw Clapton into despair.