The girls went back and forth on Twitter igniting a feud on Wednesday, which all started when Thorne said Mongeau "broke girl code."
"Tana and I are no longer good," the 21-year-old actress wrote on social media. "She broke girl code I’m over it."
Thorne is referring to Tuesday night when Mongeau hit the town with Mod Sun, who the actress recently split from.
That's when Mongeau hit back.
"????? imagine taking every time ur mad at me to twitter but then telling ppl how much u care about me," the YouTube star responded. "wtf is this b :/"
Instead of letting it go, Thorne went in for the kill, accusing Mongeau of ghosting her when she tried confronting the social media sensation.
"U legit started dating me for twitter.. how about u answer ur phone and talk to me instead of being on Twitter," the actress said.
Mongeau clapped back, denying claims she used Thorne for clout.
"dude what are you doing bella? like i have no idea why you’re mad, i’ve been texting you every minute since you tweeted, and for you to be tweeting me something as hurtful as saying I dated you for Twitter is literally fucking nuts & if you honestly think that damn i lost you," she responded.
Thorne and Mod Sun split back in April after two years together.
She announced the news by taking to IG with a heartfelt message that read, "I will always love you. All good things must come to an end."
Sun has continued to talk negatively about their breakup and Thorne since their split.
Thorne -- who came out publicly as bisexual in 2016 -- started dating Mongeau in September 2017.
Months later, the actress said they had opened their relationship to other people and that's when she also began dating Mod Sun.
In February 2019, Thorne and Mongeau parted ways.
The YouTuber has since gotten engaged to Jake Paul and plans to say "I do" in front of cameras on July 28th in Las Vegas.