Former "Today" show anchor Katie Couric admitted she felt betrayed by disgraced former co-host Matt Lauer over the allegations of sexual misconduct and assault that eventually led to his firing from NBC, according to the Associated Press.

"I know Matt thinks I betrayed him, and that makes me sad," Couric writes in her new tell-all book. "But he betrayed me, too, by how he behaved behind closed doors at the show we both cared about so much."

Katie Couric and anchor Matt Lauer on Friday, Jan. 6, 2017 (Peter Kramer/NBCU Photo Bank/NBCUniversal via Getty Images via Getty Images) (Photo by: Peter Kramer/NBCU Photo Bank/NBCUniversal via Getty Images via Getty Images)

Lauer's more than 20-year career at NBC ended with his termination in 2017 following allegations of inappropriate sexual behavior by a fellow female employee going back to 2014. Following his termination, a number of other women brought forward their own stories of misconduct by him.

Lauer has denied that he ever assaulted anyone or forced anyone to have sex.

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Couric and Lauer worked together on the "Today" show from 1996 to 2007 before she left the network to host "CBS Evening News" and "60 Minutes." 

Matt Lauer said new rape claims against him are "categorically false" and defy common sense.  (AP Photo/Richard Drew)

In her book, Couric details the last time she saw Lauer, writing that she was on a walk with her husband in the Hamptons last year when she saw Lauer driving by in a white Jeep. He passed without either acknowledging each other. 

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Couric writes about her difficulty processing the allegations against Lauer and included text messages between the two that showed how their relationship dwindled to nothing after his firing and the revelations about how he allegedly treated a young woman she had brought to NBC. 

"It nauseated me," Couric wrote. 

Katie Couric (L) of the NBC Today show chats with her co-host Matt Lauer outside NBC's New York City studios during the broadcast of the April 5, 2006 program. Couric, earlier in the show, told her audience that she will be leaving NBC to join the CBS Evening News where she will become the first woman to solo anchor a network evening newscast. The 49-year-old Couric has been on Today for the past 15 years. REUTERS/Mike Segar - GM1DSHYTTRAB

Katie Couric told Andy Cohen in 2012 that Matt Lauer "pinches me on the ass a lot." (Reuters)

"So many of us were blindsided, never imagining that a dashing, witty, beloved TV star had such a dark side," she wrote. "I’ve come to realize that Matt could be an excellent professional partner, a good friend, and a predator."

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The book, titled "Going There," is scheduled to be released on Oct. 26 and will also include details on the rivalry between Couric and fellow former morning TV host Diane Sawyer.