By Hugh Schofield
BBC News, Paris
Mr Banier was once a friend of '60s icon Samuel Beckett
A French celebrity photographer is to stand trial over allegations he took hundreds of millions of euros from one of the world's richest women.
Francois-Marie Banier is accused of exploiting the mental fragility of 87-year-old Liliane Bettencourt, heiress to the L'Oreal cosmetics fortune.
He denies the charges. A French court has set the trial for April next year.
Last week Mrs Bettencourt's daughter asked that she be placed under court authority.
A judge in the city of Nanterre ruled that Mr Banier, described by correspondents as a 62-year-old aesthete, former gigolo and befriender of rich old ladies, does have a criminal case to answer for "abuse of mental fragility".
In his youth, Francois-Marie Banier was the friend of 1960s cultural icons like Salvador Dali and Samuel Beckett.
Today he is better known as a photographer, but also as a serial charmer of society women, including Mrs Bettencourt, daughter of the founder of the L'Oreal cosmetics company.
Over the last 20 years she is reckoned to have given Mr Banier around 1bn euros worth of gifts, in the form of property, art works and life insurance policies.
But Liliane Bettencourt's largesse excited the suspicions of her daughter, Francoise, who decided that her mother - in her alleged dotage - was coming under the malign influence of the man the daughter calls the "predator".
The daughter filed a private criminal prosecution, and now the judge has ruled that the case is legitimate.
"Should a daughter who sees her weakening mother under the power of a predator, a man doing everything he can to break the bond of filial love, say nothing, do nothing?" Reuters news agency quoted Olivier Metzner, a lawyer for Francoise Bettencourt, as saying at the pre-trial hearing.
Mother and daughter are said not to be on speaking terms
Ms Bettencourt has been fighting for two years to bring charges against Mr Banier, but prosecutors have been unwilling to pursue the case as her mother has refused to submit to mental health tests.
Liliane Bettencourt has dismissed claims she was conned by a fraudster, and insists she was in full possession of her faculties.
"I am here to say on behalf of Mrs Bettencourt: 'That's enough! I am not a vegetable. You will not bend me to your will'," her lawyer George Kiejman told the court.
The judge has now ruled that she must undergo mental tests to see if she really is fragile, or as her lawyers insists, actually of perfectly sound mind.