Inside Brian Austin Green and Vanessa Marcil's Complicated Relationship History

Brian Austin Green and Vanessa Marcil have long had a rocky relationship.

On Sunday, Marcil shared an emotional message to Instagram, in which she claimed that her only child — 16-year-old Kassius Lijah, whom she shares with the actor — was cut out of Green and wife Megan Fox‘s life five years ago.

So when did Marcil and Green’s relationship turn south?

Green and Marcil started dating in the late 1990s after meeting on the set of Beverly Hills, 90210. (He played David Silver for all 10 seasons, and she joined the cast as Gina Kincaid in season 9.)

After several years of dating, the two got engaged in the summer of 2001 and welcomed son Kassius Lijah on March 30, 2002. As PEOPLE reported at the time, they planned to wed that summer.

While it’s unclear why they split, Green and Marcil called it quits shortly after Kassius’ birth, in 2003.

The next year, Green started dating Megan Fox. The pair tied the knot in an intimate Hawaii wedding ceremony in 2010. At the time, all seemed well between the former couple, as Kassius, then 8 years old, was Green’s best man.

Just two years later, it was revealed that Green had tried to sue Marcil for purported unpaid loans. According to E!, Green had been seeking $200,000 he claimed he gave Marcil during their relationship. Green claimed he had an agreement with Marcil that specified that the money was not a gift and she had to pay it back.

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However, a judge threw out the case and ruled that the actor’s statute of limitations had run out. The judge also told Marcil she could seek monetary sanctions against Green. According to the outlet, Marcil asked Green for more than $50,000.

But according to Marcil, her legal battles with Green started long before he sued her in 2012. In her Instagram post on Sunday, she claimed Green and Fox tried to get full custody of Kassuis in 2006.

“12 years ago I was served legal papers and then spent 8 years+ defending myself and my son in custody court in response to his father & his stepmother trying to get full custody (that means I would have seen my son four days a month) and then asking me to pay them child support,” Marcil wrote. “They lost that case & a civil case asking me for 200,000.”

Despite the legal drama, Marcil said she never challenged Green’s right to 50/50 custody.

“I never spoke publicly in order to protect my then young son from paparazzi that used to follow him & terrify him,” she continued. “I had also never asked for child support of any kind and had never tried to take time away from Kass’ dad seeing him. Ever. In the end they lost all of these court cases. The judge called them all ‘Frivolous’ They always had 50% custody and still did when court ended as I had and have NEVER asked for full custody.”

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According to the actress, Green, 45, and Fox, 32, “decided to completely cut Kass out of their lives”with their three sons: Journey River, 2, Bodhi Ransom, 4½, and Noah Shannon, 6.

“Kass has never met his youngest brother and is not allowed to know where his bio father, stepmother and three younger brothers live,” Marcil wrote. “Custody cases hurt the children only and the truth shall set us all free. Put the kids first you guys. There shouldn’t be a ‘more important parent’ kids love both parents equally no matter what either parent’s struggles may be.”

“Kass has been truly heartbroken since being cut out of his other families lives with NO explanation,” she concluded. “Let’s do better for our kids. Let’s share our stories.”

A rep for Green did not return PEOPLE’s request for comment.

In August, Green posted a photo of Kassuis performing in a school play in August.

“Kass playing Aladdin in a play,” he wrote, adding several smiley faces. “It was awesome.”