Speculation over the name X Æ A-12 has been a major topic of conversation since the couple welcomed the baby boy into the world on Monday, with questions over what the characters mean.
The Canadian musician -- real name Claire Elise Boucher -- previously explained that is the Elven spelling of AI, which is shorthand for artificial intelligence.
"It's just X, like the letter X. Then A.I. Like how you said the letter A then I," wrote Grimes on Thursday in response to a query on Instagram.
However, Musk told podcast host Joe Rogan a different pronunciation of the name in a conversation released Thursday, even as he credited Grimes for coming up with the moniker.
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"First of all, my partner is the one that, actually, mostly, came up with the name," the Tesla and SpaceX CEO said. "Yeah, she's great at names."
Rogan then asked how to say it, to which Musk responded: "I mean it's just X, the letter X. And then, the is, like, pronounced 'Ash'... and then, A-12, A-12 is my contribution."
This 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, and Rogan asked how it felt to have another child now.
"Actually I think it's better being older and having a kid," said Musk. "I appreciate it more. Babies are awesome."
Unfortunately for the happy parents it seems their issues with X Æ A-12 go further than disagreements over pronunciation.
The unusual choice could fall foul of state rules in California, where the couple are based, which stipulate that names can only use the 26 alphabetical characters of the English language.
For those curious about what the name means, Grimes broke down each character of the name in a post on Twitter.
She explained "X" stood for "the unknown variable," while -- AI -- was shorthand for artificial intelligence and translates to "love" in several languages.
The 32-year-old star then shared that a part of her son's name is a reference to the couple's favorite aircraft.
"A-12 = precursor to SR-17 (our favorite aircraft). No weapons, no defenses, just speed. Great in battle, but non-violent," she added. Although Musk later corrected his partner, saying it was actually "SR-71."
Grimes concluded the explanatory post on Twitter by revealing that the "A" in the name also represents "Archangel," which she described as her favorite song.