Late on a January evening in 1962, Her Serene Highness Princess Grace of Monaco is drinking heavily in her 235-room pink palace overlooking the Mediterranean.

When she gave up her Hollywood career to marry Prince Rainier — the ruler of the tiny tax haven - Grace Kelly, as she then was, believed that she had found the perfect husband.

Six years later, however — after bearing him an heir, Albert, and an elder daughter, Caroline — she is so disillusioned she has decided she will flee back home to America, where she has been offered $1 million (Dh3.68 million) to star in Marnie, a new Alfred Hitchcock thriller.

The fee — $7.6 million in today’s terms — is staggering.

But it’s not the money that has attracted her, she confides to her husband’s chaplain and closest adviser, Father Francis Tucker. Rainier’s tyrannical rules and explosive temper have worn her out, the beautiful 32-year-old tells the elderly priest.

What will happen, she asks him, if she accepts the Hitchcock role and seeks a divorce?

“Your children will suffer most,” replies Tucker. “They are heirs to a European throne. You’ll be lucky to see them again. I suppose the world will also hang its head in disappointment.”

The shock scene is taken from the script of Grace Of Monaco, a new film in which Nicole Kidman portrays Grace as the lonely and desperate victim of an abusive husband.

The project, which also stars Tim Roth as Rainier and Frank Langella as Father Tucker, was recently denounced by Grace’s son, Prince Albert, and his sisters Caroline and Stephanie, as ‘needlessly glamourised’ and riddled with ‘major historical inaccuracies and a series of purely fictional scenes’.

But the 106-page script, which has been seen exclusively by The Mail on Sunday and is registered with the Hollywood Writers’ Guild, is based on hundreds of interviews biographers have conducted over many years with palace insiders and other first-hand sources.

The family’s real fear, it seems, may be that the film has broken a long-standing Hollywood taboo about bringing the truth about the marriage to the big screen — and it may set the stage for more embarrassing projects.

While Rainier sleeps in a separate room from Grace in the script, and is said to be constantly ‘busy’ during the daytime, the production glosses over accusations that he was unfaithful.

“This film really is a very slim slice of Grace’s life and it is nowhere near as negative as it could be,” Wendy Leigh, a biographer of the princess, said last night.

According to her 2007 book, True Grace, the suave, cigar-smoking prince began cheating on Grace soon after she became pregnant during their honeymoon. Within months, he had taken at least three mistresses.

“I think the family were hoping to stop the film and that this is their warning shot to producers who might want to do the full story about Rainier’s promiscuity and cruelty,” Leigh said.

“Grace was humiliated and she was extremely unhappy. She was surrounded by decadence and Rainier’s disreputable friends.”

Blonde, blue-eyed and with a sultry sex appeal that casting directors compared to Marlene Dietrich, Grace herself was hardly an innocent.

The daughter of a socially ambitious Philadelphia brickworks owner, she became infatuated with several of her leading men.

While shooting the Hitchcock thriller Dial M For Murder in 1954, she scandalised Hollywood by conducting an affair with her married co-star, Ray Milland. She met Rainier during a photoshoot in 1955 at his palace. Six years her senior, he was seeking a wife with the help of a crony, the Greek shipping baron Aristotle Onassis, played in the film by Robert Lindsay.

His quest was a matter of urgency. If he failed to conceive a legitimate heir, Monaco would become a French protectorate under the terms of a 1918 treaty.

After she submitted to an examination to prove she was capable of bearing children, he presented her with a 12-carat diamond engagement ring. “I fell in love with Prince Rainier,” she confides in the film’s opening scene. ‘What followed was more difficult than I had thought.’

A silver Rolls-Royce delivers Alfred Hitchcock — played by Roger Ashton-Griffiths — to the palace, where he is greeted by Grace’s scheming lady-in-waiting, Madge Tivey-Faucon (Parker Posey).

Madge has been chosen for her job by Rainier — her chief qualification for the role being her willingness to spy on Grace’s every move.

Hitchcock is puzzled that there is no sign of the prince. A palace retainer quietly tells him: ‘He never comes. Far too busy.’

Speaking little French, Grace is bored and homesick, occupying herself by preparing pumpkin soup and other American dishes for Ray, as she calls Rainier in rare moments of tenderness.

The Monaco climate does not agree with her. Her eyes are reddened from conjunctivitis and she suffers from hayfever and insomnia. Hitchcock turns up just as she is composing a secret letter to her mother to confide she is miserable and wants to end the marriage.

Now Hitchcock is giving her the perfect excuse to leave in a matter of weeks. “Universal will pay you one million dollars,” he says. “It’s going to be the role of a lifetime.”

“Do I look that unhappy, Hitch?” she asks wearily.

“You look tired, Gracie,” he says.

It isn’t only Rainier’s tantrums and constant absences that have brought her marriage to the point of breakdown. As ‘his’ princess, she must submit totally to his rules which, according to the script, include smiling sweetly at his side and never voicing an opinion.

At a New Year’s Eve party on the Onassis yacht, he grows red-faced with rage when she engages French President Charles de Gaulle in a debate about the UK-US special relationship. Rainier furiously confronts her when they return home. “This is not America, Grace! People don’t just speak their minds.”

“What did you expect me to say?” she asks.

“I don’t know. You used to be an actor. Act,” he snarls.

Madge, he adds, has informed him of Hitchcock’s visit. “She is very loyal,” he reminds his wife. Pecking a kiss on her forehead, he retires for the night, closing the door to his bedroom behind him.

Some biographers claim Rainier was violent as well as a control freak. During a tennis doubles match, he allegedly aimed a ball straight at Grace’s face. When it hit her, the friend who was his doubles partner defended him, saying he was just ‘desperate to win’.

The film treads carefully on the issue. He is verbally abusive to Grace, flying into a rage when she shears her long hair into a fashionable bob. He shouts that she did not seek his permission: “It looks dreadful. It yells of disrespect.”

When Grace finally plucks up the courage to tell Rainier that she would like to accept Hitchcock’s million-dollar offer of the leading role in Marnie, he assures her: “I won’t stand in your way.”

But his words “don’t ring true”, and when her plans for the movie are leaked to the press — she suspects by palace plotters — the prince’s 30,000 subjects are horrified.

Smashing a glass he is holding to the floor, Rainier tells Grace he has changed his mind in the face of the outcry. “You’ll have to call Mr Hitchcock and turn him down,” he orders. “We’ll make a show of how happy you are here.”

“That’s not your decision to make,” she says. “I am the prince, and your husband,” he storms. “You will and you must!”

In the end, the role of Marnie went to another Hitchcock protegee, Tippi Hedren.

The film’s most contentious claim is that Grace eventually sought a divorce from Rainier.

The director, Olivier Dahan, has not identified the script’s precise sources for the claim, but they would appear to include a mysterious book, Grace: A Disenchanted Princess, published under a pseudonym in France in 2004.

It quoted one Rainier relative, Christian de Massy — whose mother, Princess Antoinette, was the prince’s sister —recalling that Grace was heartbroken when she was forbidden to do Marnie.

Despondent about life in a ‘golden cage’, she allegedly consulted an American divorce lawyer but, after being advised that she would lose her children, resigned herself to her fate in Monaco.

The royals — who were shown the screenplay when Dahan applied for permission to shoot in Monaco — claim that to their ‘astonishment’, their ‘numerous requests for changes’ were ignored.

Dahan has promised, however, that the film, which he started to shoot last August in Monaco and Paris, will be released on schedule early next year. “I think we have a misunderstanding,” he said, insisting that he neither needs the royal family’s permission, nor has sought it. “We never asked them to endorse anything,” he stresses.

The new film draws to a close when Grace stumbles on evidence that Antoinette, portrayed by Geraldine Somerville, is conspiring with France to seize control of the principality in a coup.

As part of this treacherous deal, de Gaulle has agreed that Christian, who at the time was just 13, will assume the throne.

The Mail on Sunday is withholding the exact details of the suspense-filled denouement to the purported plot — which critics claim involves considerable licence on the filmmakers’ part as Antoinette clashed with her brother in the Fifties.

One clue, however: it leads to a reconciliation between Grace and Rainier, and she bears their third and final child, Stephanie.

The screenplay ends with one simple line: “Grace Kelly never acted again.”

Worn down by disappointment, she died in a 1982 car crash, apparently after suffering a stroke.