Grimes is suing her ex-partner Elon Musk over access to their three children.
US outlet Page Six reported the 'Genesis' performer had filed a "petition to establish parental relationship" on September 29 in a California court.
The lawsuit is meant to establish the child's legal parents when their parents are not married. It can also be used to seek child support, expenses with pregnancy and custody.
Musk, 52, has yet to publicly respond to the court action.
The former couple have three children: X, three, Exa, 20 months; and baby Techno Mechanicus.
In a now-deleted tweet, Grimes, 35, made a desperate plea to "tell Elon to let me see my son or plz [please] respond to my lawyer."
It was only revealed in September that the former couple shared a third child after Time magazine published an excerpt from Musk's biography.
Grimes subsequently confirmed the child's existence online on September 11.
The pair began dating in 2018 and maintained an off-and-on relationship until September 2021.
Grimes gave birth to a son named X Æ A-Xii in May 2020 before revealing details of a daughter, who had been welcomed via surrogate in December 2021.
