Musk, 48, confirmed on Monday that he and singer Grimes, 32, welcomed a son, sharing a photo of the baby on Twitter and also revealing his name.
Just a day later, Grimes also took to Twitter to explain the meaning behind the name, indicating that it serves as references to mathematics, love, artificial intelligence, aircraft and music.
During an episode of "The Joe Rogan Experience" podcast on Thursday, Musk shared exactly how to pronounce the name.
"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 her Twitter explanation, Grimes broke down the baby's name letter by letter.
"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 on the tweet, correcting the aircraft she referenced.
"SR-71, but yes," he wrote.
X Æ A-12 is Grimes' first child. Musk shares five sons from a previous marriage. Musk's first son reportedly died of sudden infant death syndrome at 10 weeks old in 2002.
Musk and Grimes, whose real name is Claire Boucher, have been dating since 2018.