Sandy Garossino, the mother of Grimes, said in a series of unconfirmed social-media posts Saturday that Tesla CEO Elon Musk is "withholding" their children and didn't let them visit their ailing great-grandmother.

Musk and Grimes have been in a custody battle involving their three children. Representatives for Musk, Grimes and Garossino didn't immediately respond to requests for comment. For now, the details of the situation come from Garossino.

Writing on X, she said she had no other way to reach Musk other than posting on his platform, noting that her 93-year-old mother is at end-of-life care and wants to see her great-grandchildren one last time.

To celebrate their great-grandmother's birthday, the kids were supposed to visit her in Canada this weekend, but the trip was canceled, Garossino added.

"I am alarmed to learn that the children cannot come as you are withholding them and their needed passport documents from Claire," she wrote, referring to Grimes' given name. "It was even more troubling to see you and X on television at the Olympics in Paris yesterday, after your DC trip earlier in the week."

Garossino also asked Musk to "honour your agreement, return the children, and provide the documents they need to see their great grandmother before she passes."

She concluded her message by saying, "Please Elon, I beg you. This is so painful for my mother, and concerning for the kids. Time is of the essence now."

In addition to his three children with Grimes, Musk has nine other kids with other women, including ex-wife Justine Wilson and Shivon Zilis.

His estranged daughter Vivian Jenna Wilson highlighted Garossino's plea on her Threads account and blasted Musk for "keeping their children, her children, away from their mother during the most important developmental period in a child’s life."

Days earlier, Wilson, who is transgender, described the billionaire as a cruel absentee parent in an interview with NBC News after her father said she was “killed by the woke mind virus.”

“He was there, I want to say, maybe 10% of the time. That’s generous,” she said, adding that during these periods, he’d pressure her to appear more masculine.

“I was in fourth grade. We went on this road trip that I didn’t know was actually just an advertisement for one of the cars—I don’t remember which one—and he was constantly yelling at me viciously because my voice was too high,” Wilson said. “It was cruel.”

After the interview, Grimes offered support for Wilson, tweeting on Thursday that "I love and am forever endlessly proud of Vivian."

This story was originally featured on Fortune.com