"Kass has never met his youngest brother and is not allowed to know where his bio father, stepmother and three younger brothers live," wrote Vanessa Marcil

Credit: David Livingston/Getty; Jason LaVeris/FilmMagic

Vanessa Marcil is speaking out on behalf of her son.

The Las Vegas alum, 50, shared an emotional message to Instagram on Sunday, in which she claimed that her only child — 16-year-old Kassius Lijah, from a previous relationship with Brian Austin Green — was cut out of Green and wife Megan Fox‘s life five years ago.

“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,” began Marcil. “They lost that case & a civil case asking me for 200,000.”

“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” and the lives of 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 immediately respond to PEOPLE’s request for comment.

RELATED VIDEO: Vanessa Marcil Suffers Seventh Miscarriage Three Months After Announcing Pregnancy

Marcil has notably endured hardship in her quest to become a mother once more. In January, she revealed she had suffered a miscarriage — her seventh total — three months after announcing her pregnancy.

Her news came with a call for privacy and a message to others that have had a similar loss, reminding them that they are “not alone.”

“Our hearts are with Vanessa and MC who have lost baby OPM,” the caption read. “Thank you for respecting their privacy as they heal and thank you for sharing all of your personal stories. You are not alone.”