Elon Musk and Canadian singer Grimes have confirmed that they have named their baby - "X Æ A-12".
The Space X CEO announced the birth of their son on Monday writing on Twitter, "Mom & baby all good," reports BBC.
He also announced the baby's name on Twitter. Later, both Musk and his girlfriend offered an explanation to her followers on social media.
The name X Æ A-12 has been trending on Twitter with many asking how the name will be pronounced.
What does the name mean?
When Musk, known to joke on Twitter, announced the name, many people questioned whether he was being serious.
However, Grimes explained first the name's meaning to her fans.
Æ, a ligature of a and e known as ash, appeared in Latin and Old English but has mostly fallen out of use. However, in some languages such as Danish, Norwegian and Icelandic, Æ is classed as a letter.
The singer has used Æ before, naming a song on her latest album 4ÆM.
The A-12 is a Lockheed plane built for the CIA. It was known by designers during its development as Archangel.
She also claims Archangel is her favourite song but does not explain who the song is by.
It remains unclear how the name is pronounced. However, when someone on Twitter asked Musk whether it could be X Ash Archangel, Musk liked the comment, giving the biggest clue as to how it might sound.
The question about the name's legality has also arised.
It's thought that Grimes may have given birth in California where certain names cannot be registered.
The rules there stipulate that no pictographs, ideograms and diacritical marks for example è, ñ, ē, ç can be used when registering the birth. Names have to consist of the 26 letters of the alphabet.