The bitter family battle for the L’Oréal billion

As the deposit box was opened the three men present could hardly believe their eyes. It was, as one later described, "like Christmas". On the shelves of the bank vault were "rivers of diamonds" alongside emeralds, rubies, sapphires. Row after row of precious gems set into some 30 pieces of dazzling jewellery. On another shelf was a small sack containing dozens more diamonds, cut but unset.

The breathtaking cache belonged to the L'Oréal heiress Liliane Bettencourt, part of the estimated £8 billion fortune that makes her the wealthiest woman in France, 21st on the Forbes rich list and the nearest thing the French Republic has to the Queen.

The two lawyers and a bailiff in the vault of the Paris bank had been alerted by one of Madame Bettencourt's financial advisors, one of only two ­people to hold a key to the deposit box (the other is Mme Bettencourt) worried that some pieces might have gone missing.

There was just one problem: nobody could be sure what should be in the bank vault. Officially the gems and jewels did not exist and had never been included in any inventory or insurance assessment.

Today, police and investigators will begin picking over every jewel in Mme Bettencourt's secret stash after it was announced that a celebrated society photographer who befriended the wealthy widow is to stand trial accused of defrauding her of almost 1 billion.

François-Marie Banier, whose friends have included Salvador Dalí, Picasso and Yves Saint Laurent as well as actor Johnny Depp and his wife Vanessa Paradis, has been accused of taking advantage of her age and confused mental state to obtain the sum in cash, works of art and life insurance policies. The legal action for "abuse of weakness" has been brought by 86-year-old Bettencourt's only child, Françoise Bettencourt-Meyers, leaving mother and daughter barely on speaking terms.

The story of this unlikely couple — ­Bettencourt, the grande dame and Banier, nicknamed the "enfant chéri " or spoiled child — has shocked and divided the chic salons of Paris where for decades she has dazzled as brightly as her diamonds and he has charmed his way into rich and influential circles.

It is a tale containing all the usual elements — wealth, love, beauty, glamour, generosity and consequent perfidy and betrayal — except perhaps sex, because nobody is suggesting the friendship between Bettencourt and 62-year-old Banier, who is gay, was anything other than platonic.

Even so, such public airing of dirty linen has thrown up captivating details that suggest Mme Bettencourt's daughter is right to be very worried about her mother handing over a considerable part of her fortune. Staff employed at the Bettencourt family home in the rich Paris suburb of Neuilly-sur-Seine, the former fiefdom of French president Nicolas Sarkozy, have testified how the ailing and increasingly forgetful and fragile Mme Bettencourt was bullied by her friend who reportedly wanted her to adopt him as "the son she never had".

One described how when on holiday in the Seychelles in 2006 on a private island that some claim Bettencourt was planning to buy for Banier, the photographer kept harassing her to write him a cheque. One evening when they were about to go out to a party and she was putting on lipstick: "He grabbed it out of her hands and threw it against the wall, saying it was not attractive half an hour later she fell ill," said one ­member of staff.

Another story has the artist Banier being gripped by a sudden overwhelming desire to paint a landscape while in the Seychelles. Having left his brushes in Paris he asked if it would be all right to send the private jet back to Paris to ­collect them. The answer was: "Oui."

Others, however, speak warmly of Banier's allure, charisma and magnetic character. Mme Bettencourt, who owns one third of L'Oréal, has herself vigorously denied losing her mind. In an interview last year she accused her daughter of being "jealous".

"Life would be no fun if you only saw people from the same background as your own," she said.

"My daughter is rather introverted. So someone who is extroverted like François-Marie is a bit annoying for her. It's about time she realised that I'm a free woman."

She also described Banier, who has been her protégé since he was commissioned to take her photograph in 1987, as an "artist" and a man "full of ­ingenuity".

Both sides had hoped to resolve their differences discreetly. The decision by Mme Bettencourt's daughter to escalate legal wrangling into a full-blown court case has effectively dashed any hope of that, even in France where the rich and famous are able to hide behind strict privacy laws.

"I am acting in my mother's interest," is all Françoise Bettencourt-Meyers, 55, would say yesterday.

Liliane Bettencourt is the only child of L'Oréal founder Eugène Schueller, who made a fortune in 1907 with a patented hair dye he called Aureale. Her mother died when she was five and she formed a close bond with her father who never remarried. Schueller was a controversial figure, alleged to have had Nazi sympathies and to have supported the Vichy government of occupied France.

By contrast, Banier was born into a middle-class family on which he turned his back when a dark-haired, handsome but sexually confused teenager. Armed with little more than charm, good looks and wit he appears to have insinuated his way into the world of the rich, famous and artistic. He became friends with Salvador Dalí, Pierre Cardin, Yves Saint Laurent, Françoise Sagan, Samuel Beckett and others from the French beau monde.

Banier met Mme Bettencourt with the Italian film director Federico Fellini and the novelist Marguerite Duras when commissioned to take pictures of them for Egoiste magazine in 1987.

He soon became a frequent visitor to the Bettencourt family home where Liliane held court with her husband André. The couple's hospitality and exclusive salons were opened to the photographer, who had also written four novels.

Britain's own society charmer Nicky Haslam once described Banier as a "strategic master on the battlefield of charm" and none of it was lost on Mme Bettencourt whom he flattered and amused.

By 1996, she had begun transferring property into Banier's name and in 2001 she handed over titles to 11 works of art, masterpieces that allegedly included a Picasso, a Mondrian, a Delaunay, and a Matisse worth an estimated 20 million as well as a photograph entitled The Black Widow by the celebrated surrealist Man Ray. The works were to continue to hang in the Bettencourt family home but were to be given to Banier on her death.

By 2003 the "gifts" had totalled around 250 million. Another 56 million followed in cash and gifts over the next two years and in 2006 Banier was given money and valuables worth a further 250 million. To date, financial investigators estimate that in total Bettencourt has given Banier money and goods to the value of 990 million.

In December 2007, just one month after the death of her father André, Françoise Bettencourt-Meyers instigated legal action against Banier, claiming he had taken advantage of her mother's increasing frailty and weak mental state.

A magistrate was appointed to investigate and ordered Mme Bettencourt to undergo independent medical tests to establish whether she is suffering any mental incapacity. She has refused.

Her daughter has described her stubborn refusal as "Kafkaesque" and insists her mother is a victim who needs legally protecting from herself. She has also drawn from medical records that show her mother might have memory problems and disorientation.

Mme Bettencourt's own doctor has said she is in fine health but in December 2007 a French neurologist at the Pitié-Salpetrière hospital in Paris (where Princess Diana was taken after her fatal car crash) suggested, after examining Mme Bettencourt, that she might be made the French equivalent of a ward of court.

"My mother claims that she is perfectly aware of what she is doing but, curiously, she has refused to be seen by the independent medical experts demanded by the court, which would remove all doubts," said her daughter last week. "Is she really making her own decisions? I find it hard to believe."

Ms Bettencourt-Meyers's case has been supported by several witness statements from members of her ­mother's entourage including her accountant, her chambermaid and her personal nurse. These have spoken of Barnier having a "strong hold" over the l'Oréal heiress.

Several have confirmed that she regularly suffers "absence" and "loss of memory", others have spoken of witnessing the "psychological pressure" Banier has put on his friend. A former nurse, named in court papers only as Henriette Y, remembers that Bettencourt had "suffered under the pressure of M Banier who influenced her in all her decisions it was almost always a question of money in their discussions. He demanded a lot of it from Mme Bettencourt and obtained everything he wanted."

François-Marie Banier has refused to comment on the accusations. In September last year he and his companion Martin d'Orgeval were arrested but denied vigorously the accusations against them. No charges were made.

Some of his celebrity friends have jumped to his defence. The American-based designer Diane von Furstenberg said: "I've known François-Marie Banier for more than 30 years. He's a great artist and like most artists he's both weak and strong at the same time. In America he is very well liked.

"I love him deeply as a person and I admire his talent as an artist. I will always defend him. He is a man of quality and an artist who leaves a real body of work."

But Bettencourt's daughter remains convinced Banier's motives are mercenary and insists she is neither jealous nor interested in her mother's money.

The French have a saying: "Where there is possession, there is war." For more than 18 months Liliane Bettencourt's family and François-Marie Banier have battled. Now, with the public court case scheduled for ­September, it is war.