Laurence Pieau, the editor of French Closer magazine, has been formally charged in connection with an alleged breach of France's privacy laws and now faces the prospect of a humiliating trial alongside at least two photographers and her publishing director, Ernesto Mauri.
Judicial sources in Paris arrested Pieau earlier this month, but chose last night to announce her new legal position, The Telegraph reported.
They also said that an unnamed 28-year-old Paris agency photographer had been arrested and charged, while another was 'on the verge' of being charged.
Suau describes her own pictures, published in La Provence regional newspaper, as 'all decent'.
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But she is suspected of having assisted at least one other photographer who took numerous snaps of the topless Duchess.
Kate and Prince William, both 31, took legal action against Closer through their French lawyer, Aurelien Hamelle, who described the Duchess as a "a young woman, not an object".
He said the royal couple had suffered a "grotesque breach of privacy" and felt "violated" during a "highly intimate moment during a scene of married life".
Pieau, meanwhile, has given numerous interviews in which she has justified the pictures, saying in December: "I did my job as a journalist".
The photographs of the Duchess sunbathing on the terrace of Viscount Linley's Chateau d'Autet, in Provence, on September 5 last year caused a public outcry in Britain.
The French media are protected from having to name their sources, including photographers, but the royal couple are said to have made it a personal crusade to discover who took the images.
The royal couple, meanwhile, have moved on from the controversy and are celebrating the birth of their newborn son Prince George, along with the whole of Britain.