Grimes and Elon Musk have been forced to change their baby's name to comply with California law.
The 32-year-old singer - who gave birth to her son on May 4 - has revealed via Instagram that she's changed her baby's name from X Æ A-12 to X Æ A-Xii, because California law prohibits Indo-Arabic numerals in names.
The name change came to light after an Instagram follower asked: "Did you change the baby name because of Californian laws ? What is the baby's new name? (sic)"
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And Grimes replied: "X Æ A-Xii (sic)"
The music star subsequently added: "Roman numerals. Looks better tbh (sic)"
Under California law, names must be written on birth certificates "using the 26 alphabetical letters of the English language" - although apostrophes and dashes can be included, too.
Meanwhile, Grimes previously revealed she hopes her baby becomes a fan of raving.
The singer - whose real name is Claire Boucher - said: "Children need to get into raving, but I don't think I'll rave with my kid ... I don't think kids and adults need to rave together.
"But I wish I had discovered dance music at an earlier age. I don't have a problem with late bedtimes/nocturnalism. Unless there's some health risk I should know about.
"The baby has already been exposed to a lot of techno in the womb."
Grimes also revealed she wants to ensure her baby isn't "too spoiled".
She said: "I'll probably have to send them to live in the woods with my grandpa periodically so they aren't too spoiled. He's very intense. Lots of physical labour in the cold and whatnot, haha!"