"He was totally devastated," a source familiar with Matt Lauer's firing tells PEOPLE

The sexual misconduct allegations brought against Matt Lauer came as a shock to Today show audiences — and to the terminated longtime anchor.

According to a source with knowledge of the former anchor’s firing — it came after after the network received a “detailed complaint from a colleague about inappropriate sexual behavior” on Monday — “in [Lauer’s] mind, this had been a consensual affair. And a long-term one at that.” (In a statement obtained by PEOPLE, NBC News Chairman Andrew Lack said the complaint “represented, after serious review, a clear violation of our company’s standards.”)

“He was totally devastated,” the source says of Lauer. “He never thought it would get to this level.”

Lauer, 59, “was shocked and dumbfounded and completely bewildered by what happened,” says the source, who adds, “He never expected this. He had felt like he was invulnerable — like Superman.”

“People who worked with him found him to be flirtatious, but that doesn’t mean he was necessarily inappropriate,” the source shares.

In a statement provided to the New York Times, Ari Wilkenfeld, a civil rights lawyer with the firm Wilkenfeld, Herendeen & Atkinson in Washington, confirmed he represents the woman who made the complaint to NBC, but declined to publicly identify her.

“My client and I met with representatives from NBC’s Human Resources and Legal Departments at 6 p.m. on Monday for an interview that lasted several hours,” said Wilkenfeld. “Our impression at this point is that NBC acted quickly, as all companies should, when confronted with credible allegations of sexual misconduct in the workplace.”

“While I am encouraged by NBC’s response to date, I am in awe of the courage my client showed to be the first to raise a complaint and to do so without making any demands other than the company do the right thing,” he continued.

NBC announced early Wednesday that Lauer had been fired after the network received a “detailed complaint from a colleague about inappropriate sexual behavior” on Monday, with reason to believe “this may not have been an isolated incident.”

In the wake of his firing, several insiders told PEOPLE that the veteran morning host was allegedly often unfaithful to his wife of 19 years, Annette Roque, with whom he shares three children: son Jack, 16, daughter Romy, 14, and son Thijs, 11. (Lauer’s reps did not comment.)

An insider with knowledge of some aspects of the situation previously told PEOPLE that “there was most definitely more than one” affair and alleged that “they were never with anyone whom [Lauer] didn’t have significant seniority over.” (A second source formerly told PEOPLE that Lauer was fired after alleged inappropriate sexual behavior throughout 2014, including at the Winter Olympics in Sochi, Russia.)

WATCH: ‘Everyone Knew’ Matt Lauer ‘Cheated On’ Wife, but Misconduct Allegations Are ‘a Shock’: Sources

On Wednesday afternoon, Variety published a report in which three anonymous women accused the former newsman of sexual harassment, claiming Lauer had once brought a female employee into this office “and then dropped his pants, showing her his penis.” Lauer then allegedly “reprimanded her for not engaging in a sexual act.”

A former NBC employee – who spoke to the The New York Times on condition of anonymity – also came forward, saying that Lauer sexually assaulted her in 2001. According to the publication, Lauer had been making “inappropriate comments” to her after she started working at the media company in the late 1990s.

For the first time since his termination from NBC, Lauer, who is focusing on his family since he parted ways with the network, spoke out in a statement read by Guthrie on Thursday.

“There are no words to express my sorrow and regret for the pain I have caused others by words and actions,” Lauer said in the statement obtained by PEOPLE. “To the people I have hurt, I am truly sorry. As I am writing this, I realize the depth of the damage and disappointment I have left behind at home and at NBC.

“Some of what is being said about me is untrue or mischaracterized, but there is enough truth in these stories to make me feel embarrassed and ashamed. I regret that my shame is now shared by the people I cherish dearly.”

“Repairing the damage will take a lot of time and soul searching, and I’m committed to beginning that effort. It is now my full time job. The last two days have forced me to take a very hard look at my own troubling flaws. It’s been humbling. I am blessed to be surrounded by people I love. I thank them for their patience and grace.”