Brian Austin Green has heated words for his ex Vanessa Marcil.

The BH90210 actor didn't hold back when he responded to her claim that she had raised their son Kassius, now 20, by herself following their 2003 breakup. Vanessa made the allegation in a recent Q&A on her Instagram Story, in which she replied to a fan's question about the former couple's co-parenting situation: "We didn't & don't co-parent. I raised my son alone."

Posting a screenshot of the actress' answer, Brian wrote on Feb. 24, "So, I can't tell you all how frustrating it is to read continued lies from a 50+ year old woman on social media like she is still in high school. She has never in her life been someone to walk the walk. Talk is cheap."

Brian—who also shares three sons with ex-wife Megan Fox, as well as a 7-month-old baby boy named Zane with girlfriend Sharna Burgess—went on to claim that he was the one who did most of the parenting in their dynamic.

"Megan and I bust our asses to give Kass a well rounded childhood since his mom was rarely there," he wrote. "I'm assuming that's why she posts so much of him now. When will she just GO AWAY."

Brian and Vanessa, 54, started dating in 1999 after meeting on the set of Beverly Hills, 90210. They welcomed Kassius in 2002.

Almost a decade after their split, Vanessa sued Brian in January 2012 over purported unpaid loans. Her case against the Anger Management alum was dismissed months later, with a judge ruling that the statute of limitations had run out.

Drama between the duo made headlines again in 2018, when Vanessa made accusations that Brian and his then-wife Megan had "completely cut Kass out of their lives" and claimed that her son was "truly heartbroken" over the alleged situation. E! News did not receive a comment from Brian and Megan at the time.

However, the dynamic between Brian and Vanessa seemingly shifted in recent years. In July 2019, Vanessa raved about Kassius "visiting his dad in Canada" and she rooted for Brian more than two years later when he competed on the Dancing With the Stars' 30th season.

Sharing a photo of Kassius in a car on his way to the DWTS' live taping, she wrote in a September 2021 post, "Headed to see dad. #TeamGreen."

E! News reached out to Vanessa's rep for comment on Brian's latest remark but did not hear back.

For the latest breaking news updates, click here to download the E! News App