Updated at 4:48 p.m. ET

Editor's note:This story contains explicit accusations that some readers may find upsetting.

A former junior colleague of Matt Lauer's has accused him of raping her in his hotel room during the 2014 Winter Olympics in Sochi, Russia. In her first public comments about the incident — told to journalist Ronan Farrow for his forthcoming book, Catch and Kill— Brooke Nevils said the former Today show host forced anal sex on her without her consent in his hotel room.

According to NBC News, it was Nevils' complaint that ultimately led to Lauer's firing in 2017 — one of the most prominent dismissals during the #MeToo movement. Until now, the accuser's identity and her specific allegation of rape had not been publicly known.

Varietyreported Nevils' accusation Tuesday night, based on advance copies of Farrow's book. By Wednesday morning, NBC News had released a statement calling Lauer's conduct "appalling, horrific and reprehensible."

Lauer responded to the rape allegation Wednesday by sending an open letter to NPR and other news outlets in which he denied wrongdoing and said his previous silence "has been a mistake."

"Today, nearly two years after I was fired by NBC, old stories are being recycled, titillating details are being added, and a dangerous and defamatory new allegation is being made. All are being spread as part of a promotional effort to sell a book," the former NBC star wrote in a note that spans more than two pages. "It's outrageous."

In its response to the newly public details, NBC News said it feels the same horror it did "at the time" the agency first learned of the allegations, adding, "That's why he was fired within 24 hours of us first learning of the complaint."

The current anchors of the Today show also addressed their predecessor's alleged conduct in a somber segment on-air.

"This is shocking and appalling, and I honestly don't know what to say about it," Savannah Guthrie said, her voice quavering.

Of Lauer's accuser, Guthrie said, "I know it wasn't easy for our colleague Brooke to come forward then; it's not easy now. And we support her and any women who have come forward with claims."

"It's very, very, very difficult," she added.

In Farrow's book, Nevils details the evening on which the alleged sexual assault took place. She says Lauer joined her and Meredith Vieira, Lauer's former Today co-host, in a hotel bar in Sochi during the Olympics, for which NBC is the U.S. broadcaster and partner. Nevils says that later that night, after she had consumed many drinks, Lauer summoned her to his hotel room to retrieve her media credential.

She recounts him pushing her onto his hotel bed, asking if she liked anal sex, and despite her repeated refusals, raping her anally.

"It was non-consensual in that I was too drunk to consent," she told Farrow in his book. "It was non-consensual in that I said, multiple times, that I didn't want to have anal sex."

In his response, Lauer, 61, said he had "an extramarital, but consensual, sexual encounter" with Nevils in 2014, in which "we engaged in a variety of sexual acts" — but he insists, "each act was mutual and completely consensual."

That night in Sochi, Lauer asserted, was the start of an affair that continued after they returned to New York City, including a "sexual encounter" in his dressing room. "That showed terrible judgment on my part," Lauer added, "but it was completely mutual and consensual."

He said that he broke off the affair and that he did not learn of any complaint from her until called in to speak to an NBC News attorney in November 2017, shortly before his firing.

Nevils' newly surfaced allegations, he added, "cross a serious line."

"Because of my infidelity, I have brought more pain and embarrassment to my family than most people can ever begin to understand. They've been through hell. I have asked for their forgiveness, taken responsibility for what I did do wrong, and accepted the consequences," Lauer said. "But by not speaking out I also emboldened those who continue to do me harm with false stories."

You can read the full letter here.

In the book, Nevils acknowledges that she told Lauer that she was OK with what happened between them. But she adds that she did so to preserve her job and that of her boyfriend's brother, who worked for the NBC star. And she says she had several further sexual encounters with Lauer.

Nevils says that although she tried to convey to Lauer that she was fine, she told partial accounts about him to colleagues and, according to Farrow, she reported Lauer's behavior to a new boss at Peacock Productions — a different TV unit within the greater NBC network.

Catch and Kill delves deeply into the incidents and background of the investigative reporting that won Farrow a Pulitzer Prize last year. Farrow's October 2017 report in the New Yorker on disgraced Hollywood megaproducer Harvey Weinstein — along with a separate investigation by The New York Times' Jodi Kantor and Megan Twohey — has been credited with propelling the #MeToo movement that brought the downfall of dozens of prominent men accused of sexual misconduct.

Farrow left NBC in 2017 over the network's refusal to broadcast his reporting on allegations of Weinstein's serial sexual assaults and abuse. In his book, Farrow reports that seven women told him of incidents of sexual misconduct by Lauer and that he also uncovered seven nondisclosure agreements with former NBC News employees to silence accusations against Lauer.

Some of the agreements involved monetary payments, which in Nevils' case was seven figures.

Farrow also reported that NBC News executives were spooked by the possibility that the National Enquirer, allied with Weinstein, might report seedy allegations about Lauer — and even allegations about the behavior of former NBC News Chairman Andrew Lack years earlier, during his tenure at CBS.

In a statement issued Wednesday afternoon, Lack asserted that Lauer was fired within 24 hours of the company's learning of his conduct and that "any suggestion that we knew prior to that evening or tried to cover up any aspect of Lauer's conduct is absolutely false and offensive."

And Lack disputed Farrow's explanation of why NBC did not proceed with his piece.

"After seven months, without one victim or witness on the record, he simply didn't have a story that met our standard for broadcast nor that of any major news organization. Not willing to accept that standard and not wanting to get beaten by the New York Times, he asked to take his story to an outlet he claimed was ready to publish right away. Reluctantly, we allowed him to go ahead," Lack said.

"Fifty-three days later, and five days after the New York Times did indeed break the story, he published an article at the New Yorker that bore little resemblance to the reporting he had while at NBC News."

Just over a month after the initial stories about Weinstein appeared, NBC News fired Lauer after receiving what the network described as a "detailed complaint from a colleague about inappropriate sexual behavior in the workplace."

On Wednesday, Hoda Kotb, who replaced Lauer as Todayco-anchor early last year, said during the show that she, and all of Lauer's former colleagues, are struggling to digest the latest news.

"We don't know all the facts and all of this, but they are not allegations of an affair; they are allegations of a crime. And I think that's shocking to all of us here who have sat with Matt for many, many years," Kotb said. "So I think we're just going to continue to process this part of this horrific story."

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