Elon Musk and Grimes have a new nickname for their baby X Æ A-Xii.
The couple sparked huge debate earlier this year when they announced their son’s very unique name.
Their baby boy, who they call X for short, now has another unusual name.
Singer Grimes, 32, says she and her SpaceX billionaire boyfriend, 49, call him “c”, as in the speed of light.
The moniker is perhaps a nod to his rate of development, as at just five months old, Grimes says her baby boy is already quite the critic, with plenty of strong opinions.
She told the New York Times: “I’ve watched Apocalypse Now and stuff with my baby.
“He’s into radical art. Like, he just actually is, and I don’t think it’s problematic to engage with them on that level.”
Grimes, whose real name is Claire Bloucher, says her baby has even helped her create a new song.
She said: “The first version, there was too many sort of sharp bells, and it caused tears and just general chaos. X would smile more and stuff…
“I was basically personally just referencing ambient music I’ve heard, and then kind of trying to make it cuter. It’s a bit sparklier, a bit nicer.”
Tesla founder Elon has previously admitted that Grimes plays a much bigger part in their son’s life at the moment than he does, but he’s looking forward to the things they can do together when he’s older.
He once told The Times: “Well, babies are just eating and pooping machines, you know? Right now there’s not much I can do. Grimes has a much bigger role than me right now.
“When the kid gets older, there will be more of a role for me.”
Elon and Grimes’ son was originally named X Æ A-12, but they had to change it for legal reasons.
They weren’t legally allowed to put X Æ A-12 on the birth certificate, despite them obviously being allowed to call their baby whatever they want.
A supervisor at the Department of Public Health Vital Records Office, Los Angeles is said to have told that it’s illegal to include symbols and numbers in names on birth certificates in the state of California.
That’s believed to be why they changed it to X Æ A-Xii.