Now, the duo is offering up even more confusion as their pronunciations of the name appear to be different.
"First of all, my partner's the one that actually mostly came up with the name," he explained. "It's just 'X,' the letter 'X,' and the 'Æ' is pronounced 'ash' and then 'A-12' is my contribution. Archangel 12, the precursor to the SR-71, coolest plane ever."
In an Instagram post from Thursday, May 6, however, the 32-year-old musician offered a different take.
A fan commented on her photo -- a pair of pictures from her photoshoot with Italian Vogue -- asking "how do you pronounce the baby's name?"
Grimes, whose real name is Claire Boucher, replied to the comment.
"It's just X, like the letter X," she wrote. "Then A.I. Like how you said the letter A then I."
Grimes previously offered an explanation of the meaning of X Æ A-12's name.
"X, the unknown variable," the singer wrote, adding an emoji of two crossing swords. "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," she continued, adding a white heart emoji. "(A=Archangel, my favorite song) (metal rat)."
Musk later commented, correcting the airplane his girlfriend referenced.
"SR-71, but yes," he wrote.
X Æ A-12 is Grimes' first child. Musk shares five sons from a previous marriage and his first son reportedly died of sudden infant death syndrome at just 10 weeks old in 2002.
Musk and Grimes have been dating since 2018.