Elon Musk and Grimes have changed their baby's name to X Æ A-Xii

(CNN) — Just when you thought you'd learned how to spell Grimes and Elon Musk's unusual baby name, they've gone and changed it.

Earlier this month, Tesla and SpaceX CEO Musk announced the birth of the baby boy in a post on Twitter, revealing his son was called "X Æ A-12 Musk."

However, speculation arose that the unusual moniker might fall foul of the law in California, where the couple live, as names can only use the 26 alphabetical characters of the English language, according to the state constitution.

READ MORE: Elon Musk and Grimes' complete relationship timeline

On Sunday, Grimes posted a new photo on Instagram, drawing comments from fans.

"Did you change the baby name because of Californian laws ? What is the baby's new name?" asked one Twitter user in the comments under the latest post.

"X Æ A-Xii," wrote the singer in response, without confirming the reason for the change.

The singer also responded to another comment, saying: "Roman numerals. Looks better tbh."

Grimes previously broke down the meaning of the name for intrigued fans.

The Canadian musician — real name Claire Elise Boucher — explained 'X' stands for "the unknown variable".

Meanwhile, 'Æ' is the Elven spelling of AI, which is shorthand for artificial intelligence and the word for 'love' in several languages, including Japanese.

"A-12 = precursor to SR-17 (our favorite aircraft). No weapons, no defenses, just speed. Great in battle, but non-violent," she added.

The 'A' in the name also represents 'Archangel', which she described as her favourite song.

Fans were also intrigued as to how to pronounce the name, and the happy couple seem to have different interpretations.

"It's just X, like the letter X. Then A.I. Like how you said the letter A then I," Grimes wrote in response to a query on Instagram.

However, Musk told podcast host Joe Rogan a different pronunciation of the name.

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

X Æ A-Xii is the couple's first child together. Musk has five other children — twins Griffin and Xavier and triplets Damian, Saxon and Kai — from a previous marriage.

By Jack Guy, CNN