Making a slight change to the name of their newborn, Tesla CEO Elon Musk and his singer girlfriend Grimes have now named their first child X AE A-Xii. 

The difference is only in the numeral part of the name which is now written in the Roman format.

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.'

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

'A-12 = precursor to SR-17 (our favourite 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 AI 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.