Citing the memory of her dead brother, Carla Bruni, France's first lady, today put her celebrity power at the service of the cause of Aids, becoming an ambassador for the main international fund fighting the disease.

The model-turned-singer, who married President Sarkozy in February, confirmed that her deep interest in Aids relief had been spurred by the death of Virginio Bruni-Tedeschi, who died of the disease in July 2006.

"Because of my brother, of course I am very sensitive to the issue of Aids," she said. "This is a pandemic. We tend to forget, we are used to it. But look at the figures. It's staggering.

"I can put all of the media coverage directed toward me to the service of a useful cause," Ms Bruni told Elle magazine in an interview to mark the event and World Aids Day.

Ms Bruni dedicated her latest album to her brother, a photographer, designer and long-distance yachtsman, who died in Paris at 46. She has said that she still suffers from his absence. She addresses him in one of the tracks in her latest album, called, Salut Marin (Bye Sailor): "You are taking away with you/ All our childhood of crystal/ And our youth of honey/ And our rainbow plans," she sings. The cause of Virginio's death was known in France but Ms Bruni had not publicly alluded to it before.

The 40-year-old Première Dame was the draw at a packed news conference at a state mansion beside the Elysée Palace, at which she was anointed ambassador by the Global Fund to Fight Aids, Tuberculosis and Malaria. The Geneva-based organisation, backed by the United Nations, has channelled $8 billion (£5.4 billion) into fighting Aids since 2002.

Reading timidly from a text, Ms Bruni said that her decision to devote herself to the Aids cause was not just by chance. "It is the extension of something that I have already done with my family," she said. She would focus on Africa and in particular she would "try to help women and children because they are the most vulnerable victims." The world has become complacent about the disease but women and children in Africa were dying because they feared the stigma attached to it, she added.

Ms Bruni plans to travel often to Africa, where her family are already promoting Aids education through a fund set up last year in the memory of Virginio. Marisa Bruni Tedeschi, their mother, raised €18.7 million (£15.9 million) for the fund by selling the antique collection of her late husband Alberto.

Royalties from the new album, called Comme si de rien n'était (As if nothing had happened) after one of her brother's photographs, have largely gone to Aids charities.

Ms Bruni's decision to make Aids her main mission follows a tradition in which French presidential wives have pursued worthy causes. Bernadette Chirac raised funds for children's medical care. Aids campaigners were delighted with her decision because "the Carla effect" is vastly greater than the star power of any of her predecessors.

Ms Bruni, who hails from the wealthy leftwing elite, cultivates a demure, discreet public style and has barely put a foot wrong since her whirlwind romance and marriage to the newly divorced president last winter. Her latest triumph came from appearances on US television to promote her record last week.

At home, Ms Bruni's apparent perfection, modesty and her less than stellar singing talent, have begun drawing a little mockery. Today's front-page cartoon in Le Monde had her being banned from state television for advertising her songs. Nicolas Canteloup, a comic impersonator with a highly rated breakfast radio slot, now satirises her by imitating her with a near-inaudible speaking and singing voice.

She has also been drawn into a feud between le Canard Enchaîné, the satirical weekly, and two journalists who have written a book claiming that she is the true source of a spoof "Carla's Diary" which it publishes on its front page. The newspaper denies the claim.

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