Matt Lauer has also been accused of sexting female staffers at NBC, allegedly sending lewd messages and revealing pictures to women including a young intern.

Sources tell Page Six that the reason he was fired so quickly by NBC News is that the messages, saved by an NBC employee whom he approached while they were in Sochi, Russia, for the 2014 Winter Olympics, “showed incontrovertible proof of inappropriate sexual behavior on his part.”

It is believed the first woman to come forward and complain about Lauer is a junior production worker who was at the 2014 Sochi Olympics as an intern, where she was first approached by Lauer.

NBC News President Andy Lack said in a meeting with staff Wednesday that Lauer’s involvement with the woman, who has not been named but is still an NBC employee, continued after they returned to New York.

A source told Page Six, “There’s at least one picture [sent to her by Matt] which was a major part of the evidence, which is why the firing came so quickly … my understanding was it was so damning that it was unquestionable whether or not he should be fired.

“I think everyone was a bit surprised how quickly this all turned around. No one expected his termination to happen that quickly. I believe the silver bullet was the photo and that was so damning that they had no other option but to fire him.

“Plus, the girl had a high-power attorney and so everyone knew if NBC didn’t make a decision and push it out quick, they would have arranged for a sit-down interview with a competitor [and the messages could be made public]. Matt took the news well once he realized he was in a corner. He was very apologetic.”

Lauer’s spokesperson declined to comment, as did his personal attorney when approached numerous times by Page Six. NBC reps also declined to comment on his alleged sexting.

Since news of Lauer’s firing broke Wednesday morning, two other women have come to NBC with claims against Lauer, one of whom claimed the $25 million-a-year anchor summoned her to his office for sex, telling the New York Times she “felt helpless because she didn’t want to lose her job.”

Lauer will not be missed by some of his co-workers. Former MSNBC host Keith Olbermann tweeted: “Matt Lauer was remorsely vindictive and tyrannical to everyone at NBC News and management repeatedly enabled him and buried the issue.”

Numerous other current and past “Today” staffers also expressed surprise at NBC chief Lack’s claim that this was the first complaint against Lauer in 20 years, with one insider telling us, “Everybody knew about Matt’s behavior, and everyone had to put up with it because he was so powerful, and well protected by management.”

But an NBC spokesperson said, “We can say unequivocally that, prior to Monday night, current NBC News management was never made aware of any complaints about Matt Lauer’s conduct.”

A spokesperson for former NBC News boss Jeff Zucker, who now runs CNN, also insisted there were no complaints about Lauer under his reign.