One day in 1993, the financier Jeffrey Epstein brought a model named Stacey Williams to Trump Tower in Manhattan to say hello to the building’s owner, Donald J. Trump. As he and Mr. Epstein chatted, Mr. Trump groped Ms. Williams, she said.

Ms. Williams, a former Sports Illustrated swimsuit model, made the accusation this week in an interview with The New York Times and on a Zoom event in which several women said they had been victims of sexual misconduct by Mr. Trump. The women, some of whom had previously made their allegations in public, endorsed Vice President Kamala Harris for president.

The Times spoke to two of Ms. Williams’s friends, who said she had previously told them about the assault. Mr. Trump’s campaign denied on Friday that it ever happened, calling the allegations “unequivocally false” and politically motivated.

Ms. Williams is the latest of more than a dozen women to accuse the former president of sexual abuse and misconduct. Last year, for example, a New York jury found him liable for sexually abusing and defaming the writer E. Jean Carroll, who said Mr. Trump raped her in the dressing room of a department store. Mr. Trump was also once caught on tape boasting about assaulting women.

At the time of the 1993 incident, Ms. Williams was dating Mr. Epstein, who would later be convicted as a sex offender and in 2019 killed himself in his jail cell after being arrested on federal sex-trafficking charges. The two had met in 1992, at a party with models and Wall Street types at a restaurant on Manhattan’s Upper East Side. Ms. Williams said that she sat next to Mr. Epstein and that they talked about politics.

Later in 1992, Ms. Williams bumped into Mr. Epstein again at a Christmas party that Mr. Trump hosted at the Plaza Hotel. A relationship developed over the next several months.