In his first interview since being suspended from NBC Nightly News, Brian Williams admitted to and apologized for past mistakes, telling TODAY's Matt Lauer, "I said things that weren't true."

"It has been torture," Williams said, of the months since he was suspended. "Looking back, it has been absolutely necessary. I have discovered a lot of things. I have been listening to and watching what amounts to the black box recordings from my career. I’ve gone back through everything — basically 20 years of public utterances."

An extensive review by NBCUniversal into Williams' reporting in the field and commentary from a period of more than 10 years found that he made a number of inaccurate statements about his role and experiences in covering events in the field. Williams, who has been suspended since February, opened up about what he says has been a difficult period.

"I was reading these newspaper stories, not liking the person I was reading about, wanting — I would have given anything to get to the end of the story and have it be about someone else, but it was about me. These statements I made, I own this; I own up to this and I have to go through and see and try to figure out how it happened."

On Thursday, NBC announced that Williams would not return as the anchor of Nightly News, naming Lester Holt as the show's permanent anchor. Williams will join MSNBC, where he was an anchor from 1996-2004, as an anchor of breaking news and special reports, beginning in mid-August.

"Brian now has the chance to earn back everyone's trust," Andrew Lack, Chairman of NBC News and MSNBC, said in a statement Thursday. "His excellent work over twenty-two years at NBC News has earned him that opportunity."

"I am a grateful person,'' Williams said. "I am fully aware of the second chance I have been given. I don't intend to squander it."

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In his sit-down with Lauer, Williams reflected on what made him tell inaccurate stories from the course of his 22-year career.

"It had to have been ego that made me think I had to be sharper, funnier, quicker than anybody else,'' he said. "I told the story correctly for years, before I told it incorrectly. I was not trying to mislead people, (and) that to me is a huge difference. It came from a bad place. It came from a sloppy choice of words. I told stories that were not true. Over the years, looking back, it is very clear I never intended to. It got mixed up, it got turned around, in my mind.

"This came from clearly a bad place, a bad urge inside me. This was clearly ego-driven, a desire to better my role in a story I was already in. That’s what I’ve been tearing apart and unpacking and analyzing."

After going through his past public comments, Williams acknowledged instances in which he made mistakes.

"I said things that were wrong,'' he said. "Looking back, with such clarity now, it is so clear to me, I said things that were wrong. I told stories that were wrong. It wasn’t from a place where I was trying to use my job and title to mislead. I got it wrong. I own this, and I own up this.

"One is too much. Any number north of zero is too many. We can't have it. I can’t have that in my life. I can’t have that in my work. I can’t have that in the company we work for."

Williams is looking forward to seizing a second chance and working toward regaining the viewers' trust.

"I will work every day for it,'' he said. "I'll go person by person. All I can tell people is, 'Hold me to account. Judge me by as harsh a standard as you wish. Many already have. That's fair."

He also has made peace with the fact that he will not return as anchor of NBC Nightly News.

"Was it my first choice? No,'' he said. "Obviously I wanted to return to my old job. I thought we'd had a great 10-year run and were on top for most of that time. I pushed back at first. Enough time has passed, I accept the decision.

"There's another component here, and that is our friend Lester Holt. No one is more deserving. This game came in under the worst circumstances and has upheld everything great about the place and the broadcast. It's Lester's job."

Williams also is thankful to be returning to NBC.

"I'm very happy to be coming back,'' he said. "First of all, I'm happy to have a job. I'm happy to work. I'm very fortunate to be able to go back to NBC. What I said earlier about the second chance club, I'm now its leading spokesman."