The French president, Emmanuel Macron, and his wife plan to present scientific evidence to a US court to prove that Brigitte Macron was not born a man, the lawyer representing them in a defamation suit has said.

The couple filed the suit in July against Candace Owens, a rightwing influencer, and her business, alleging continuing defamatory attacks against them in order to boost the profile of her media platform, gain more audience and make money.

Owens said last year she would “stake [her] entire professional reputation on the fact that Brigitte Macron is in fact a man” named Jean-Michel Trogneux, and has since doubled down on the false claim, including in an eight-part podcast series.

The Macrons’ lawyer, Tom Clare, of the law firm Clare Locke, which has won several high-profile defamation cases, told the BBC’s Fame under Fire podcast that Brigitte Macron had found the claims “incredibly upsetting” and they were a “distraction” for the French president.

Candace Owens said last year she would ‘stake [her] entire professional reputation on the fact that Brigitte Macron is in fact a man’. Photograph: Octavio Jones/Reuters

Clare said: “Expert testimony will come out that will be scientific in nature.” He did not reveal what nature the testimony would take, but said the couple were prepared to demonstrate fully, “both generically and specifically”, that the claims were untrue.

“It is a process that she will have to subject herself to in a very public way,” he said. “But she is firmly resolved to do what it takes to set the record straight.” Photos of Brigitte pregnant and raising her children would be presented, he added.

The Macrons’ suit states that Trogneux is Brigitte’s older brother and lives in Amiens, northern France, where he grew up with Brigitte and four other siblings. He attended Emmanuel Macron’s presidential inaugurations in 2017 and 2022.

Brigitte Macron, 72, is 24 years older than her husband, whom she met at a theatre workshop that she was running at his high school. She has three children from her previous marriage, born in 1975, 1977 and 1984, and seven grandchildren.

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Claims she was born male first went viral in France in 2021. Brigitte and Trogneux won a defamation case against two bloggers, Amandine Roy and Natacha Rey, but an appeals court has since ruled the case did not fit the legal definition of defamation.

Brigitte Macron and her brother have taken the case to France’s highest court. The case against Owens alleges she “disregarded all credible evidence disproving her claim in favour of platforming known conspiracy theorists and proven defamers”.

The influencer’s lawyers have responded with a motion to dismiss, arguing that the case should not have been filed in Delaware, where her businesses are incorporated, since it did not relate to them. Owens has insisted she stands by her allegations.