Former UFC champion Ronda Rousey recently revealed the reason for her sudden retirement from MMA fighting in 2016, saying that a string of concussions made it necessary for her to walk away.

In an Instagram Live interview on Thursday promoting her upcoming memoir, "Our Fight," Rousey revealed why she left the sport after a Dec. 2016 loss to Amanda Nunes by TKO.

"My concussion history that I had to keep secret for years so I would be able to continue to compete and perform, that's basically why I had to retire," the former UFC women's bantamweight champion said.

Rousey, 37, was being interviewed by her sister and co-author Maria Burns-Ortiz, who asked Rousey to share facts that fans don't know about her.

The 2008 Olympic Bronze medalist in judo had never lost an MMA fight until she faced Holly Holm at UFC 193 in Dec. 2015, defending her UFC title six consecutive times. Holm knocked Rousey out with a kick to the head.

Rousey spoke about that fight publicly for the first time on Thursday.

"I think that there was just so much to [my feelings about that loss], that I couldn't talk about it in the form of like an interview or an article or anything like that, or there would be several filters between my words and people reading it," she said.

"So much had to do with having so many concussions when I was in judo before I even got into MMA, I couldn't talk about it at all when I was doing MMA because it would literally put a target on my head, and I might not have been allowed to compete any further," she said.

After retiring from the UFC, Rousey continued to dabble in acting and performed in the WWE from 2018 to 2023. But even then, she felt that publicly sharing her concussion history could have jeopardized her wrestling career.

"Same thing with WWE. They have a complicated history with their performers getting concussions, and it would be a bad look on them. So I felt like I really couldn't talk about it at all," Rousey said.

"Our Fight" hits shelves on April 2.

With reporting by TMX