“[Bill] O’Reilly’s suggestion that no one ever complained about his behavior is false,” Megyn Kelly said during “Megyn Kelly Today.” “I know because I complained.” (Charles Sykes/Invision/AP)

Megyn Kelly on Monday waded back into territory she vowed to leave behind, saying on her new NBC morning program that she complained about Bill O’Reilly while she was an anchor at Fox News but was ignored.

In an extraordinary monologue, Kelly went after O’Reilly, her former bosses and colleagues, accusing the network of fostering a toxic culture for its female employees.

“O’Reilly’s suggestion that no one ever complained about his behavior is false,” Kelly said during “Megyn Kelly Today.” “I know because I complained.”

Kelly has vowed to keep her program light and sunny, but the revelation Saturday that O’Reilly paid $32 million to a Fox contributor, Lis Wiehl, to settle harassment allegations in January drew her back into a topic she might have wanted to avoid.

In November, two months before she left Fox for NBC, Kelly emailed Fox’s co-presidents, Bill Shine and Jack Abernethy, to object to O’Reilly’s comments during a CBS News interview, she said. O’Reilly said at the time that he wasn’t “interested” in discussing a topic — sexual harassment — that “makes my network look bad.”

In response, Kelly said, she wrote to her bosses: “Perhaps he didn’t realize the kind of message his criticism sends to young women across the country about how men continue to view the issues of speaking out about sexual harassment.

“Perhaps he didn’t realize his exact attitude of shaming women into shutting the hell up about harassment on grounds that it will disgrace the company is in part how Fox News got into the decade-long [Roger] Ailes mess to begin with. Perhaps it’s his own history of harassment of women which has, as you both know, resulted in payouts to more than one woman, including recently, that blinded him to the folly of saying anything other than, ‘I am just so sorry for the women of this company, who never should have had to go through that.’ ”

She said the response was that O’Reilly was “permitted with management’s advance notice and blessing” to appear on his program that night “to attack the company’s harassment victims yet again.”

Kelly also took a shot at Fox News’s chief media relations officer, Irena Briganti, saying she had abetted Fox’s attack on those who had complained about harassment. Briganti “is known for her vindictiveness,” Kelly said. “To this day, she pushes negative articles on certain Ailes accusers like the one you’re looking at right now,” meaning Kelly herself.

The Washington Post's Margaret Sullivan discusses how sexual harassment allegations at Fox News are changing workplace culture. (The Washington Post)

“This must stop,” she said. “The abuse of women, the shaming of them, the threatening, the retaliation, the silencing of them after the fact, it has to stop.”

The harassment scandal at Fox exploded in July 2015 after former anchor Gretchen Carlson accused network co-founder and chairman Ailes of harassing her. Her lawsuit, which Fox settled for $20 million, led to the ouster of Ailes. Subsequent revelations took down O’Reilly, Shine and general counsel Dianne Brandi and led to millions of dollars in settlements with women who made claims. Abernethy and Briganti remain at Fox.

Briganti had no comment Monday. Fox’s parent company, 21st Century Fox, released a statement saying: “21st Century Fox has taken concerted action to transform Fox News, including installing new leaders, overhauling management and on-air talent, expanding training, and increasing the channels through which employees can report harassment or discrimination. These changes come from the top, with Lachlan and James Murdoch personally leading the effort to promote civility and respect on the job, while maintaining the Company’s long-held commitment to a diverse, inclusive and creative workplace.”

The company also said, “Irena is a valued colleague and she has our full support.”

In response to Kelly, O’Reilly’s spokesman, Mark Fabiani, released two handwritten notes from Kelly to O’Reilly. The first is a note thanking him for his presence at her baby shower in 2009. “What a class act you are,” she wrote, adding, “You’ve become a dear friend and I am grateful to have you in my life.”

The second note thanks O’Reilly for mentioning the latest book by her husband, Doug Brunt, on his program. She wrote: “I appreciate how supportive you have been of me here [at Fox]. You are a true friend and mentor.” (Kelly’s office said that note was from 2012.)

Kelly’s comments were her first about Fox since she began her NBC program, which has struggled in the ratings. They were largely out of character for the upbeat tone she said she wanted to set.

Her statement preceded an interview with former Fox News anchor Juliet Huddy, who claimed that she had been harassed by O’Reilly and Abernethy while working at the network. Huddy quietly settled her claims against the network in September of last year, reportedly for a sum in the high six figures.

Kelly was also speaking out following a report by the New York Times that O’Reilly had paid Wiehl $32 million to settle harassment allegations spanning 18 years.

Kelly — who privately lodged a harassment complaint about Ailes while at Fox — has gone public about harassment at Fox before, most notably in her book “Settle for More,” published in November.

During her interview with Huddy and her attorney Douglas Wigdor, Kelly opined that O’Reilly’s settlement with Wiehl was “so shocking . . . because it was made after Ailes was gone and after [Fox was] trying to improve the culture, and they knew he had settled five other cases.”

Following her interview with Huddy, Kelly went back to the lighter fare that has been the hallmark of her show since its debut. She conducted an interview with former talk-show host Phil Donahue and then did a segment with the author of a book about crockpot cooking.