Grimes, also known as Claire Boucher, filed a lawsuit against Elon Musk, alleging he's denying her access to one of their children.
The dispute revolves around their youngest child, Techno Mechanicus, born secretly last year.
Grimes' legal action is common in cases of unmarried couples sharing children and typically includes requests for child support and custody agreements.
Both Grimes' attorney and Musk declined to comment.
Grimes and Musk dated from 2018 to 2021 and have two other children, X Æ A-Xii and Exa Dark Sideræl.
Grimes described her relationship with Musk as the "best internship ever."
Elon Musk has a total of 11 children with three different women, including twins born in 2021.
Musk has been a prominent advocate for having children.
His first child, Nevada, died of sudden infant death syndrome in 2000.
Grimes' legal action highlights a dispute over parental rights and access to their child Techno Mechanicus.