Credit: ABC News

Former boxing heavyweight champ Mike Tyson said his role in "The Hangover," the hit 2009 film about three groomsmen and their drunken Vegas debauchery, actually helped him become sober and get his life back on track.

Tyson, who has had three stints in rehab for substance abuse, said he was still in a "dark place" when the movie was filming. But after it came out, he said one day he was swarmed by a tour group full of kids, who hugged him and asked him all sorts of questions about his "Hangover" performance, in which he played himself as the owner of a stolen white Bengal tiger.

"That changed everything for me, which I'm so appreciative," Tyson, 46, said. "That was just some good stuff."

In a brutally honest interview with "Nightline" anchor Terry Moran, Tyson opened up about his turbulent past, dealing with substance abuse and moving forward. The champ said he has been sober for over three years now, but still grapples with his demons every day.

"I'm just constantly working on turning. It doesn't happen overnight," he said. "I may have a good few years in me but it's still not out of me. You still have to work consistently. Every moment of the day you have to work because your demons always - that's who you are."

After years of reigning supreme in the boxing ring, Tyson's career has been marked by struggle and heartache. Tyson served a three-year sentence in the '90s for a rape conviction, a crime he still denies he committed.

"I didn't do that," Tyson said. "I'm never going to say I did something I didn't do… I'm just so happy that it's over."

The champ's boxing career then suffered another major blow in 1997 when he bit off part of Evander Holyfield's ear during a fight. He has been married three times, and has sought treatment for his issues with drugs and alcohol abuse.

"Being in rehab, that kicks you're a-," he said. "If you really trying to do this thing and you have your demons still banging on you and you want to do the right thing, this is kicking you're a-, it's kicking you're a-, I don't care how tough you are… it's killing you but you have to do it."

Then in 2009, Tyson's 4-year-old daughter Exodus Tyson died in a treadmill accident at her home in Phoenix, a devastating loss that still pains the champ today.

"I'm traumatized," he said. "But I know if I dwell on it, I'll be a psychopath."

Tyson now has two young children with his third wife Lakiha Spicer. He is on a vegan diet and said he is "constantly working" on turning over a new leaf.

From the boxing ring to center stage, Tyson is about to embark on a new adventure on Broadway - a one-man show about his life called, "Mike Tyson: Undisputed Truth," directed by Spike Lee. The show will run 12 times between July 31 and Aug. 12.

"I like to describe it as me just being naked onstage, not physically naked, but just naked spiritually and emotionally onstage," Tyson said.

But despite all the good that has come to him in recent years, the champ said he believes he could still fall off the wagon.

"I have to always believe it can happen to prevent it from even going in that direction," he said. "I'm so weak… [but] I see my faults, I know my flaws, I know my faults, and I'm dealing with those issues in my life to improve my life."

Credit: Kizzy Cox/ABC