Earlier this month, the Tesla CEO, 48, and the singer, 32, left their fans perplexed when they revealed that they named their newborn son X Æ A-12.
But in an Instagram post on Sunday, Grimes was asked by a fan if she had changed her son's name, given that the moniker reportedly won't be accepted by the state of California.
Grimes confirmed so writing back to the fan, "X Æ A-Xii," although she did not give clarification on the reason for the name change.
When another follower wrote to Grimes, "Nice! Just removed the numbers to confirm to California law," she responded, "Roman numerals. Looks better tbh."
Although the original name of X Æ A-12 is technically legal, family law attorney David Glass recently told PEOPLE that Califonria only accepts the use of the 26 characters in the English language for baby names.
"Thus, you can't have numbers, Roman numerals, accents, umlauts or other symbols or emojis," he said.
Glass also explained that if X Æ A-12's birth certificate is submitted as-is, it is sure to be rejected and that the couple will "have an opportunity to appeal the rejection of the birth certificate application but it's unlikely that it will be granted."
Elon Musk Twitter Elon Musk and son X Æ A-12
Grimes — whose birth name is Claire Boucher — and Musk welcomed their son on May 4.
The new mom previously gave fans some insight into what their son’s unique name meant, explaining on Twitter that X represents “the unknown variable” and "Æ, my elven spelling of Ai (love &/or Artificial intelligence).”
She went on to share that part of the name is a nod to the CIA's Lockheed A-12 reconnaissance plane, which has “no weapons, no defenses, just speed. Great in battle, but non-violent.” The "A" in the name also represents "Archangel" — which she said is her "favorite song" — while the number "12" stood for the Chinese zodiac sign of the rat.
She also broke down the pronunciation of the name, telling one Instagram user earlier this month: “It’s just X, like the letter X. Then A.I."
Taylor Hill/Getty Images Grimes (L) and Elon Musk
However, Musk offered up a different pronunciation during a recent episode of The Joe Rogan Experience podcast. While he revealed that Grimes was actually the one who "mostly came up with the name," Musk said that X is spoken "like the letter" while "the 'Æ' is pronounced like 'ash.' "
During the show, Musk also proudly proclaimed that the A-12 part of his son's name was his idea, saying that he wanted to pay homage to the Lockheed A-12.
"A-12 was my contribution," he said. "The Archangel-12, the precursor to the SR-71, the coolest plane ever."
This is the first child for Grimes, while Musk has five sons from a previous marriage. His first son, Nevada, died tragically of SIDS at 10 weeks old in 2002.