Grimes is suing Elon Musk to establish a “parental relationship” with one of their three children, according to the New York Post. Details of the lawsuit remain under seal, but TMZ speculates that it revolves around their youngest child, Tau, after Grimes said that Musk will not allow her to visit one of their children.

Last month, Grimes posted on X — the site formerly known as Twitter — that she was pursuing some sort of legal action against Musk. “Tell Elon to let me see my son or plz respond to my lawyer,” she wrote in a response to Walter Isaacson, who was promoting his biography of the Tesla CEO.

The lawsuit, filed September 29th in California, is meant to establish the child’s legal parents when their parents are not married. A “petition to determine parental relationship” can also be used to seek child support, expenses with pregnancy, and custody. The Post says the Grimes hasn’t asked for custody or child support, but TMZ speculates that could be a next step. Musk has not yet responded, per the reports.

Musk and Grimes had their first son in 2020. They had a daughter via surrogate in 2021, a few months after breaking up. Isaacson revealed in his biography of Musk that the two had a third child in 2022. In 2021, Musk had twins with Shivon Zilis, an executive at Neuralink, one of Musk’s companies; he didn’t tell Grimes about the twins when they were born, according to Isaacson’s book.