She was one of the most beautiful actresses ever to step on set but Hollywood star Loretta Young went to her grave in 2000 with a dark secret.

In 1935, the actress was working on a film called Call of the Wild with Clark Gable, then 34 and married to his second wife Maria 'Ria' Franklin Prentiss Lucas Langham.

The pair became close during filming and, shortly after the film wrapped, Young discovered she was pregnant - and went to great lengths to cover it up.

Fateful: Loretta Young (left) pictured with Clark Gable (right) in a scene from Call of the Wild

But while the truth about the paternity of her daughter Judy became public before her death, the real story about the circumstances of the little girl's conception have only just emerged.

Young, a devout Catholic with a strong sense of right and wrong, was, according to her daughter-in-law Linda Lewis, the victim of a date rape at the hands of Gable.

According to Lewis, the revelation came after watching an episode of Larry King Live in which the topic was discussed.

Afterwards, the then 85-year-old Young asked Lewis to explain what date rape meant. On hearing her daughter-in-law's reply, she said: 'That’s what happened between me and Clark.'

Lewis, who has since told her story to Buzzfeed journalist Anne Helen Petersen, was horrified but says for Young, the priority was always protecting Judy.

The same fear kept the family quiet as well but following Judy's death aged 78 in 2011, Lewis and her husband Chris, Young's son by her second husband Tom Lewis, decided to go public.

Secret: Young gave birth to a daughter by Gable - rumoured at the time to be because of an affair

Secret daughter: Young, pictured with her daughter Judy, gave birth to the child in secret

Tragedy: Now Young's daughter-in-law Linda Lewis has revealed that instead of an affair, Young was 'date raped' by Gable during a lengthy train journey

'Judy is not here to be hurt by this,' explains Lewis. 'And that’s what Loretta really wanted to avoid — because who doesn’t want to be conceived in love?'

Young, who had begun her acting career as a four-year-old child, was one of Hollywood's brightest young stars when she met Gable in 1935.

The nine-week shoot for Call of the Wild took place near Mount Baker, in a stretch of wild countryside three hours drive from Seattle.

According to Lewis, Young was prone to 'falling a little bit in love' with her co-stars and spent much of the shoot flirting with Gable who, in return, called her 'my girl'.

But flirtatious though Young might have been, she was a strict Catholic who had been badly hurt a few years earlier after eloping with and then divorcing her first husband Grant Withers.

She also enjoyed a lengthy - if unconsummated - affair with Spencer Tracey, a fellow Catholic who, although separated from his wife, was unable to divorce.

Young, terrified of going to Hell and with warnings from the family priest ringing in her ears, would flirt but never succumbed to advances from her co-stars.

That, however, was about to change. On the train back to Los Angeles from Seattle, the cast were, as Lewis tells it, given separate compartments.

Somewhere between Seattle and Los Angeles, Gable entered her compartment and, a month later, a humiliated Young discovered she was pregnant.

Next came one of the most elaborate cover-ups in Hollywood history, with Young going to extraordinary lengths to keep her condition a secret.

Hidden away in an apartment in L.A's Venice Beach, she eventually gave birth to a daughter, breaking the news to Gable in a telegram that read: 'BEAUTIFUL, BLUE-EYED, BLOND BABY GIRL BORN, 8:15 THIS MORNING'.

Gable, who was not named on the little girl's birth certificate, ignored the missive and never had any real involvement in Judy's life.

Secret: Young went to extreme lengths to cover up the birth of her daughter and eventually 'adopted' her

Successful: Young, pictured her in 1947 with Princess Margaret, went on to become enormously successful

Revelation: Young, pictured in 1986, told her daughter the truth of her father's identity when she was 23 but never spoke about the circumstances of her conception and was determined to ensure she never found out

Not interested: Gable, pictured with Vivien Leigh in 1939's Gone with the Wind, did not play a role in Judy's life and reportedly ripped up the telegram telling him of the little girl's birth

Young, however, was making plans to bring her daughter into the fold and arranged to 'adopt' the child - even giving an interview on the subject to a sympathetic newspaper.

Despite her best efforts, rumours of an affair with Gable continued to circulate, with the truth about Judy's paternity becoming something of an open secret.

In the end, Young finally told her daughter the truth of her parentage when she was 23 and demanding to know. Gable had, by this point, died aged 59 ten days after suffering a heart attack.

What Judy never discovered were the real circumstances of her conception - something that Lewis has finally agreed to discuss following a spate of high profile historic rape cases.

'I realized that it’s almost every day,' she explained in an interview with Buzzfeed. 'All these rapes, and the men just keep getting away with it.'