The alleged incident, subject of an anonymous letter, took place in 1998 in Washington, DC.

The Senate Judiciary Committee has asked Supreme Court nominee Brett Kavanaugh, about a fourth allegation of sexually aggressive behavior toward women, according to NBC News. Kavanaugh is alleged to have a shoved a woman up against a wall “very aggressively and sexually” while he was drunk.

The accusation, which was made anonymously, states that there were at least four witnesses to the incident. Colorado Republican Sen. Cory Gardner’s office, which received the allegation in a letter, said the letter “contained no names, no address, and no contact info.”

Senate aides asked Kavanaugh about the incident in a Tuesday phone call. He denied it, and he has continually denied the other three claims of misconduct and assault.

“We’re dealing with an anonymous letter about an anonymous person and an anonymous friend,” Kavanaugh said on the call, according to a transcript released by the Senate Judiciary Committee. “It’s ridiculous. Total Twilight Zone. And no, I’ve never done anything like that.”

Senate Republicans released Wednesday evening a copy of the letter containing the new allegation.

The fourth allegation differs from those of Christine Blasey Ford, Deborah Ramirez, and Julie Swetnick in one important way: The alleged actions took place much more recently. The previous three incidents allegedly happened in high school or college. The fourth alleged incident occurred in 1998. That year, Kavanaugh turned 33, and he worked from April 27 until December 1 as an associate independent counsel under Kenneth Starr, investigating President Clinton for lying about his affair with Monica Lewinsky.

Here is the full description of the alleged incident, from NBC’s Kasie Hunt, Leigh Ann Caldwell, and Heidi Przybyla:

According to an anonymous complaint sent to Republican Sen. Cory Gardner of Colorado, Kavanaugh physically assaulted a woman he socialized with in the Washington, D.C. area in 1998 while he was inebriated. The sender of the complaint described an evening involving her own daughter, Kavanaugh and several friends in 1998. “When they left the bar (under the influence of alcohol) they were all shocked when Brett Kavanaugh, shoved her friend up against the wall very aggressively and sexually.” “There were at least four witnesses including my daughter.” The writer of the letter provided no names but said the alleged victim was still traumatized and had decide to remain anonymous herself.

Ford alleges that Kavanaugh was drunk when he tried to force himself on her during a high school party and Ramirez says that both she and Kavanaugh were drunk in their freshman dorm at Yale when he pulled out his penis and shoved it in her face. Julia Swetnick, the third accuser, says that Kavanaugh drank excessively while sexually harassing women in high school.

Kavanaugh and Ford are scheduled to testify before the Senate Judiciary Committee on Thursday beginning at 10 am.

This post has been updated with a statement from Cory Gardner’s office and a copy of the original anonymous letter.