The daughter of Brigitte Macron told a French court that unsubstantiated claims about her mother's gender had adversely affected the French first lady's health.
Tiphaine Auziere, aged 41, spoke on the second day of the trial in Paris of ten people accused of cyberbullying the 72-year-old first lady.
If convicted, they face up to two years in prison.
"She's constantly having to pay attention to what she wears, how she holds herself because she knows that her image can be distorted," Ms Auziere said.
The recycled disinformation had led to a "deterioration" in her mother's health, she added.
The claim has long targeted the presidential couple, alongside criticism of their quarter-century age gap.
The first lady, aged 72, has not attended the Paris trial of 10 defendants - eight men and two women, aged 41 to 65 - accused of harassing her online, who if convicted face up to two years in prison.
Brigitte Macron told investigators the rumour had greatly impacted her and her family, especially her grandchildren who were told their grandmother was a man.
The first lady's lawyer had asked her daughter Tiphaine Auziere to testify.
The French first lady filed a complaint in August 2024 that led to an investigation into cyber-harassment and arrests in December 2024 and February 2025.
Among the defendants is Aurelien Poirson-Atlan, aged 41, a publicist known on social media as "Zoe Sagan" and often linked with conspiracy theory circles, who claimed on the sidelines of the trial yesterday that he was the one being harassed.
Jerome C, agged 55, told the court he was exercising his right to "freedom of speech" and "satire" when he posted or re-posted on social media.
Bertrand S, aged 56, had on Sunday said the trial was targeting his "freedom to think" faced with the "media deep state".
Previous case
The defendants also include a woman already the subject of a libel complaint filed by Brigitte Macron in 2022: Delphine J, aged 51, a self-proclaimed spiritual medium who goes by the pseudonym Amandine Roy.
In 2021, she posted a four-hour interview with self-described independent journalist Natacha Rey on her YouTube channel, alleging Brigitte Macron, whose maiden name is Trogneux, had once been a man called Jean-Michel Trogneux, the name of her brother.
The two women were ordered to pay damages to Brigitte Macron and her brother in 2024 before the conviction was overturned on appeal. The first lady has since taken the case to the country's highest appeals court.
Delphine J refused to speak to the court yesterday, saying she had already spoken at length on the matter.
Emerging as early as Emmanuel Macron's election in 2017, the claims have been amplified by far-right and conspiracy theorist circles in France, and in the United States, where transgender rights have become a hot-button issue at the heart of American culture wars.
The presidential couple filed a US defamation lawsuit in July against conservative podcaster Candace Owens, who produced a series titled "Becoming Brigitte", claiming she was born a man.
The couple are planning to offer "scientific" evidence and photos proving that the first lady is not transgender, according to their US lawyer.
Several of those on trial in Paris shared posts from the US influencer.
