Grimes and Elon Musk have changed their baby's name to comply with California law.

The 32-year-old singer, who gave birth to her son on May 4, was forced to changed her newborn's name from X Æ A-12 to X Æ A-Xii, because in Californian law you can't register a name that contains numbers. The new parents switched out the numbers for Roman numerals.

The name change was addressed after an Instagram follower asked the Delete Forever singer: ''Did you change the baby name because of Californian laws? What is the baby's new name? (sic)''

Grimes, real name Claire Boucher, replied: ''X Æ A-Xii (sic), and later added: ''Roman numerals. Looks better tbh (sic)''

In a recent interview on the Joe Rogan Experience podcast, Musk elaborated more on the origin of the unique moniker, saying its pronounced X Ash Archangel.

"First of all, my partner is the one who, mostly, actually came up with the name," the SpaceX founder said.

"I mean it's just X, the letter X. And then the Æ is, like, pronounced 'ash'... yeah... and then A-12 is my contribution. 

X Æ A-Xii is the couple's first child together Musk's seventh. He shares all six children -- Nevada, Damien, Saxon, Griffin, Xavier and Kai -- with his first wife, Justine, who he was married to from 2000 to 2008.