For some, even back in the more permissive days of the Seventies, it didn’t feel quite right to call the Woody Allen film Manhattan a ‘romantic comedy’. The central romance in question was, after all, about a twice-divorced, 42-year-old comedy writer who has an affair with a 17-year-old schoolgirl.

The besotted young lover was played by a teenage Mariel Hemingway, and the middle-aged lothario by Allen — the first in a series of films he’s made about much older men who fall for very young women.

Allen puts much of himself and his life into his films, and yesterday it finally emerged where he got his inspiration for Manhattan, widely regarded as one of his finest pictures.

Pictured, Woody Allen and his ex Mia Farrow in Rome Italy in 1983

Just three years before the film came out in 1979, Allen, then 41, embarked on a secret eight-year affair with an under-age girl. Babi Christina Engelhardt was a green-eyed, blonde, 16-year-old, high-school student and aspiring model when she met Allen in a New York restaurant, after which they began an affair.

She says it was four years later, when she was 20, that she was introduced to Allen’s new girlfriend, Mia Farrow.

They started having drug-fuelled threesomes, she has told the Hollywood Reporter magazine.

But that wasn’t the first time. Engelhardt claims that, about a year into their relationship, Allen recruited two other ‘beautiful young ladies’ for threesomes.

Engelhardt says she had experimented with bisexuality and found her experiences with Allen ‘interesting’.

In an unpublished memoir, she writes that she ‘felt sick’ and wanted to leave when Allen suggested a threesome with Mia Farrow.

She was upset and jealous that he described the film star as his new ‘girlfriend’ because she thought she was his steady girlfriend.

Halfway through their time together, Babi Christina Engelhardt the pair began having threesomes, a 'handful' of which were with Mia Farrow

However, she says she became fond of Farrow, bonding over shared cannabis joints and a mutual love of animals. The actress and activist has since fallen out spectacularly with Allen and now brands him a child molester.

‘There were times the three of us were together, and it was actually great fun,’ Engelhardt writes.

‘We enjoyed each other when we were in the moment. She was beautiful and sweet, he was charming and alluring, and I was sexy and becoming more and more sophisticated in this game.

‘It wasn’t until after it was done when I really had time to think of how twisted it was when we were together . . . and how I was little more than a plaything.’

She believed Farrow, fresh from a divorce from the conductor Andre Previn, ‘was doing this because he [Allen] wanted it’.

She adds: ‘While we were together, the whole thing was a game that was being operated solely by Woody so we never quite knew where we stood.’

Neither Allen nor Farrow have commented on her claims.

16-year-old model Babi Christina Engelhardt embarked on a hidden eight-year affair with Woody

Although Ms Engelhardt insists she is not trying to hurt Allen and has ‘no regrets’, her tawdry revelations about his having an affair with a 16-year-old schoolgirl — in an American state where the age of consent is 17 — will only compound the enormous pressure he is already under over his controversial private life, especially in a post-Weinstein age.

The Oscar-winning actor and director has already been spurned by much of Hollywood over allegations — which he strongly denies — that he sexually abused Mia Farrow’s seven-year-old adopted daughter, Dylan, in 1992.

At the time, he and Farrow were going through an acrimonious break-up after he left her for another of her adopted daughters, Soon-Yi Previn, who was 21, but still 36 years younger than him.

It isn’t the first time Allen has been embroiled in sexual scandal over the film Manhattan. Mariel Hemingway has accused her director and co-star of trying to seduce her, too, when she was a teenager and became the unwilling object of his obsession while they were filming.

Although Ms Engelhardt — now a 59-year-old divorced mother-of-two living in Los Angeles — insists she isn’t trying to jump on the #MeToo anti-sexual harassment movement and condemn Allen’s behaviour, she admits they had an unequal relationship.

She told the Reporter: ‘I was pretty enough, I was smart enough, I was non-confrontational, I was non-judgmental, I was discreet, and nothing shocks me,’ she said.

She was, however, stunned when she watched Manhattan — which Allen wrote and directed during their relationship.

She notes that she and Hemingway’s character, Tracy, were enormously similar: almost the same age, both aspiring actresses, both interested in photography and both — to the surprise of others — in love with a man not nearly as attractive as them.

In the film, the couple go to the same restaurant where Ms Engelhardt first met Allen, and — as he did with her in real life — Allen’s character, Ike, insists his young lover goes home each night.

‘He always did the same with me, although he would have his driver sending me away in his white Rolls-Royce,’ she says.

However, unlike Tracy, who is paraded in front of her lover’s approving friends on the big screen, Ms Engelhardt’s existence was kept very secret from Allen’s friends.

‘The curtains were always drawn,’ she says of her visits to his home overlooking Central Park. ‘But I wasn’t there for the view.’

Mariel Hemingway As Tracy And Woody Allen As Isaac Davis In The Film 'Manhattan

She said they had two unspoken rules: they couldn’t discuss his work and they would only meet in the seclusion of his home. She says she went there at least 100 times.

She also says that when she told Allen she’d noticed the similarities between the film and their own relationship, he replied: ‘I thought you would.’ However, she was deeply upset by what the film revealed of Allen’s feelings for her — in the movie, his character regards his relationship with his naïve teenage lover as nothing more than a fling and, much to her sorrow, he eventually dumps her.

‘I cried through most of the movie, the dawning of realisation slowly settling in as my greatest fears crept to the surface,’ writes Ms Engelhardt, who hails from a family of German emigres, and whose father was a teenage conscript into Hitler’s army.

Providing a further unhelpful connection for the embattled Allen, Ms Engelhardt reveals she also worked as an assistant for Jeffrey Epstein, the convicted paedophile financier and friend of the Duke of York.

Epstein, who kept an entourage of nubile young women, was jailed for importuning an underage girl for prostitution.

On his release from prison, he held a homecoming dinner in New York — at which guests included Woody Allen, a good friend. For years, actors were happy to work with Allen, dazzled by his talent and reputation.

Woody Allen And Mariel Hemingway In A Scene From 'Manhattan

But in an era when tolerance of predatory male behaviour in Hollywood has run out, the accumulating scandals have earned him virtual pariah status in the industry.

In 2015, Mariel Hemingway, granddaughter of Ernest Hemingway, claimed she was 17 (less than half Allen’s age) when he became completely smitten with her after they finished the filming of Manhattan.

He flew out to her parents’ home in Idaho to see her and repeatedly asked Hemingway to go to Paris with him, she said in her memoirs. The teenager, who says she was so inexperienced that she was embarrassed by the sex talk in the film, said his insistence made her increasingly nervous.

‘Our relationship was platonic, but I started to see that he had a kind of crush on me,’ she said.

She warned her parents that she ‘didn’t know what the arrangement was going to be, that I wasn’t sure if I was even going to have my own room’.

When she confronted Allen with the question, he said he ‘wasn’t sure’ if she was going to have her own room in Paris. He left the next morning and she never worked for him again.

American actress Stacey Nelkin has also claimed to have inspired the seedy Manhattan love affair. She says she was 17 when — on the set of his 1977 film Annie Hall — she started an affair with Allen. She said he seemed unbothered by their age difference during their two-year relationship, even carrying her schoolbooks when they were out together. Allen has admitted they did have a sexual relationship, but said that she wasn’t underage.

According to Babi Christina Engelhardt, the sensitive question of her age never came up with the Hollywood star, although she admits that Allen knew she was still at school.

They met one night in 1976 in the celebrity restaurant Elaine’s. Ms Engelhardt says she made the first move, dropping her number on Allen’s table after spotting him gazing at her. She wrote: ‘Since you’ve signed enough autographs, here’s mine!’

He soon rang and invited her to his home. Within weeks, they were sleeping together, she said. Ms Engelhardt says she became increasingly frustrated with Allen as she realised he didn’t share her view that she was ‘special’ in his life. As proof of their affair, she provides examples of letters and postcards he sent her.

Several of her friends told the Hollywood Reporter they were aware of her affair at the time, and one of them used to drive her to the assignations.

Ms Engelhardt says she last heard from Allen in 2001, when he sent her a letter thanking her for sending him a copy of a documentary she had made about the director Federico Fellini. ‘I hope you’re happy and well,’ he wrote. ‘I recall our times together fondly. If you’re ever in New York I would love you to meet my wife — she’d like you.’

She told the Hollywood Reporter that she assumed, given their past sexual adventures, that her meeting with Allen and wife Soon-Yi wasn’t meant to be platonic.

‘I already had children then. I was like — not that I’ve gone square, but my priorities were different,’ Ms Engelhardt said. ‘I just wanted to stay away from that.’

With his talent for self-pity, Allen recently said bitterly he should be a ‘poster boy’ for the #MeToo Movement. After reading the latest extraordinary claims about him, even diehard fans may be tempted to agree.