Ronda Rousey is finally owning up to a mistake she made more than a decade ago ... formally apologizing for sharing a Sandy Hook conspiracy theory vid back in 2013.

The former UFC bantamweight champion infamously reposted the clip -- which questioned the authenticity of the tragic school shooting that took the lives of 20 children and six staffers -- to her social media page ... before almost immediately taking it down amid backlash.

She appeared to try to sweep it under the rug in the ensuing years ... but when her recent Reddit AMA thread was bombarded by comments about the controversy -- she took to X to officially issue a mea culpa.

In a lengthy statement, she said, "I apologize that this came 11 years too late, 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."

She added, "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."

Rousey -- who, at the time 11 years ago, called the video "extremely interesting" and a "must-watch" -- explained she only reposted the footage because she was "horrified at the truth" and was "grasping for an alternative fiction to cling to instead."

Rousey also stated she first wanted to include an apology in her memoir -- which was released in 2015 -- but claimed her publisher "begged me to take it out, saying it would overshadow everything else and do more harm than good."

"So I convinced myself that apologizing would just reopen the wound for no other reason than me selfishly trying to make myself feel better," she said, "that I would hurt those suffering even more and possibly lead more people down the black hole of conspiracy bulls*** by it being brought up again just so I could try to shake the label of being a 'Sandy Hook truther."

Rousey finished her statement by advising everybody to avoid falling "down the black hole of bulls***" conspiracy theories.