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Teddy Atlas, an assistant who worked under Hall of Famer trainer Cus D’Amato, revealed for the first time Tuesday night his violent response to a sexual assault incident involving a then 15-year-old Mike Tyson and a relative during ABC’s documentary, "Mike Tyson: The Knockout." 

The incident caused a breakup between Tyson and Atlas. It happened when the legendary boxer sexually assaulted Atlas’ sister-in-law. Atlas revealed in the documentary that the incident occurred after Atlas was married and Tyson touched his new sister-in-law inappropriately.

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"I knew what I was prepared to do," Atlas said in the documentary. "I was going to kill him if I had to… He saw me coming. I just called him a piece of crap. And I put the gun to his head and I told him that he will never go near anybody in my family again. And I said, ‘you understand?’"

Atlas added that Tyson made a smirk-like facial expression, and that’s when he felt like he needed to make a statement.

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"I saw that and I stuck the gun in his ear," Atlas continued. "I started to pull the trigger and at the last second, I pulled it out of his ear. And I fired the gun then he fell on the floor grabbing his ear."

Following that incident in 1982, Atlas decided to leave D’Amato’s camp.

Years later, Tyson discussed the incident in his autobiography "Undisputed Truth."

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"I was just playing around and I grabbed her butt and I shouldn’t have," Tyson said in the book. "It was just a stupid thing to do. I didn’t think it through… As soon as I did it, I immediately regretted it."