Ronda Rousey wants Justin Bieber to apologize for being rude to her sister Julie De Mars (not pictured) at the Cannes Film Festival in October. Pictured: Ronda Rousey at a UFC press event in Melbourne, Australia, on Nov. 13, 2015. Getty Images

It's safe to say Ronda Rousey is not a Belieber, at least not right now. The 28-year-old said she isn't cool with Justin Bieber because the pop star dissed her little sister, Julia De Mars.

Rousey told TMZ Thursday that if the 21-year-old singer ever wants to be friends he has to apologize to De Mars.

Rousey and Bieber's little feud started in October when the singer supposedly refused to take a picture with the MMA fighter's younger sibling. At the time, Rousey told Cosmopolitan that she had brought De Mars to the Cannes Film Festival, and her sister was really excited to see Bieber taking photos with fans just a few feet away from them.

Rousey said she approached Bieber to ask for a picture, but the singer brushed her off.

“I walked over there and said ‘excuse me,’ and he turns to me and goes, ‘I’ve already taken a billion pictures today, OK,’” she said. The UFC Women's Bantamweight Champion said she tried to ask the “What Do You Mean” singer again if he could take a quick photo with her sister but he walked away from her.

On Thursday, TMZ asked the fighter if there's a chance she would ever be cool with Bieber but Rousey didn't seem to sure.

“He could make it up to my little sister," she said. "If she could forgive him, then I definitely would as well. I’m a protective big sister. If you’re going to be mean to my little Julia, I’m sorry then it’s just we’re not gonna be cool until you fix it.”

Rousey is extremely close to De Mars, telling The Mary Sue in 2012 that she always tries to set a good example for the teenager.

“I have the burden of having a little sister who thinks I’m the coolest thing since sliced bread and that really makes me take a second look, because everything I do she thinks is cool… When I think about being a role model I think about how I want my little sister to see me.”