The former Ultimate Fighting Championship superstar Ronda Rousey has issued her most detailed apology yet for having once engaged in Sandy Hook school shooting denialism after Reddit users inundated her with criticism during a question-and-answer session on the platform.

Rousey on Tuesday was participating in one of the Ask Me Anything discussions that celebrities frequently have with Reddit users when she was quickly flooded with questions and disapproval about her having spread misinformation baselessly challenging the veracity of the 2012 attack in Newtown, Connecticut, that killed 20 schoolchildren and six adults.

The retired mixed martial artist addressed those comments in a statement on Friday that called her decision to use one of her social media accounts to boost a Sandy Hook conspiracy theory video in 2013 “the single most regrettable decision of my life”.

“I didn’t even believe it but was so horrified by the truth [about Sandy Hook] that I was grasping for an alternative fiction to cling to instead,” Rousey said.

Rousey’s statement alluded to how she took down her reposting of the video – which she initially hailed as “extremely interesting and must-watch” – when she was met with backlash. She also apologized tepidly by writing: “I never meant to insult or hurt anyone, sorry if anyone was offended, it was not my intention in the least.” But she realized by then “the damage was done”, she said on Friday.

As Rousey told it, she had lost count of the times that she had drafted and “redrafted” the apology released on Friday. She said she had been reluctant to publish it in case it would inadvertently draw more attention to lies about the Sandy Hook mass murder.

Rousey, 37, also said she wanted to include a version of the longer apology in her recent memoir Our Fight, but her publisher successfully “begged” her to cut it from the finished product out of fear that it would be detrimental rather than helpful.

“I apologize this came 11 years too late,” Rousey’s statement on Friday said. “But to those affected by the Sandy Hook massacre, from the bottom of my heart and depth of my soul I am so, so sorry for the hurt I caused.

“I can’t even begin to imagine the pain you’ve endured and words cannot describe how thoroughly remorseful and ashamed I am of myself for contributing to it. I’ve regretted it every day of my life since and will continue to do so until the day I die.”

The video that Rousey apologized for recirculating came out at a time when far-right conspiracy theorists aggressively spread false claims that the Sandy Hook killings were a hoax carried out by crisis actors amid a government plot to force gun control on Americans. Among the most prominent of those conspiracy theorists was Infowars provocateur Alex Jones, who faces paying $1.5bn in lawsuit judgments over his peddling of Sandy Hook falsehoods.

Rousey began gaining notice from the sports world by winning a bronze medal in judo at the 2008 Olympic Games, four years after securing gold at the discipline’s 2004 world junior championships.

She is best known for having reigned as the inaugural women’s bantamweight champion in the UFC. Citing a perilous history of concussions, she retired from the UFC in 2016 and earned induction into the promotion’s hall of fame two years later.

Since her UFC retirement, Rousey has been a headlining performer for World Wrestling Entertainment while also landing work in film and television.

• This article was amended on 26 August 2024 to include the number of adults killed at Sandy Hook.