Grimes is suing Elon Musk for parental rights to their children.
The 'Genesis' hitmaker - who split from the Tesla founder in September 2021 following a three year on/off romance - filed a petition to "establish parental relationship" for their kids X, three, Exa aka Y, 20 months, and baby Techno Mechanicus, who is known as Tau, in a California court on 29 September, documents obtained by the New York Post newspaper's PageSix column revealed.
The request intends to have the court identify the legal parents of a child when they were not married.
The docket for the case is public but the filings have been sealed, but it doesn't appear that the 52-year-old Tesla boss has yet responded to the 35-year-old singer's petition.
The move comes weeks after Grimes - whose real name is Claire Boucher - hinted there were problems between her and both Elon and Shivon Zilis, the mother of the billionaire's 19-month-old twins.
In a now-deleted post shared to X, she wrote: "Tell Shivon to unblock me and tell Elon to let me see my son or plz respond to my lawyer.(sic)"
But the 'Crystal Ball' singer revealed three days later that things are amicable between her and Shivon.
She wrote on the platform on 10 September: "Hey, I wud prefer to not breathe any more life into this current press cycle but I want to de-escalate the narrative atm.
"I spoke with Shivon at length finally, which was long overdue. This wasn't her fault, plz don't be angry at her! We respect each other a lot and we're excited to become friends and have the kids grow up together.
"Women are so often pitted against each other. Speaking with Shivon, it's very evident she's an amazing human and we both just want what's best for our kids.(sic)"
She also admitted she wished she could show "how cute little Techno is" following the revelation in Elon's biography that they had had a third child together, but stressed her priority is currently keeping her kids "out of the public eye".
Shivon later responded to Grimes and praised the singer as a "total bada**".
She wrote: "At the end of the day it all ended up for the best!
"Thank you for taking the time to really connect and understand each other. So glad we had such a wonderful talk, was insanely overdue. You're a total badass and I respect you very much as well. I can't wait for kiddo play date and congrats on baby Tau as well!(sic)"
Elon also has six children with ex-wife Justine.