Grimes' and Elon Musk's baby name, X Æ A-12, is illegal in California

Fans are already confused about the name of Elon Musk and Grimes' baby son - and now it turns out the unusual name won't be legal in California.

The 32-year-old singer Grimes tweeted that their son's name, X Æ A-12, was partly inspired by the couple's favourite aircraft, according to the Daily Mail.

"A-12 = precursor to SR-17 (our favourite aircraft)," she wrote, but Musk was quick to correct her, pointing out that the spy plane is actually called an SR-71.

"I'm recovering from surgery and barely alive so may my typos b forgiven but, damnit. That was meant to be profound," Grimes, who gave birth on Monday, replied to her partner.

She explained the inspiration behind the unusual name on Twitter, saying each character represents something that is special to them as a couple.

•X, the unknown variable ⚔️
•Æ, my elven spelling of Ai (love &/or Artificial intelligence)
•A-12 = precursor to SR-17 (our favorite aircraft). No weapons, no defenses, just speed. Great in battle, but non-violent 🤍
+
(A=Archangel, my favorite song)
(⚔️🐁 metal rat)

— 𓏲Gℜiꪔ⃕es 𓆤ஐ (@Grimezsz) May 6, 2020

"X [represents] the unknown variable, Æ is the elven spelling of Ai (love &/or artificial intelligence)."

The final symbol in the name refers to the A-12 aircraft, as the A additionally stands for Archangel, Grimes' favourite song.

But the spelling isn't the only issue the couple is facing. As their son is believed to have been born where they live in Los Angeles, Musk and Grimes won't be able to register his name there. California law requires that names only include the 26 letters of the English alphabet, meaning they cannot legally register his name as X Æ A-12.

When Elon Musk’s kid comes up on the class roll pic.twitter.com/rN3PrxN4WX

— WhitePeopleHumor (@whitememejesus) May 6, 2020

Neither Grimes nor Musk have revealed how to pronounce their son's name.

Twitter users were quick to share their confusion over the name.

"That's going to be tough on the teacher," wrote one, with another joking "It's pronounced Rachel."

"That awkward moment when all names are taken, so you smash all the keys on the keyboard," commented another.