Elon Musk introduced his and Grimes‘ baby boy X Æ A-12 to the world on Twitter in May 2020. They later modified the spelling of his name in order to meet California’s legal guidelines, which only permit letters from the English alphabet. Switching over to roman numerals, the parents agreed to spell his name, X Æ A-Xii.

“X, the unknown variable,” Grimes explained on Twitter. “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.”

Grimes continued, “A=Archangel, my favorite song” with an accompanying a rat and sword emoji. “Metal rat.”

In March 2022, she announced they had welcomed daughter Exa Dark Sideræl Musk via surrograte.

“Exa is a reference to the supercomputing term exaFLOPS (the ability to perform 1 quintillion floating-point operations per second),” she said. “Dark, meanwhile, is ‘the unknown. People fear it but truly it’s the absence of photons. Dark matter is the beautiful mystery of our universe.'”

Sideræl—pronounced “sigh-deer-ee-el”—is “the true time of the universe, star time, deep space time, not our relative earth time,” she said, and a nod to her favorite Lord of the Rings character, Galadriel, who “chooses to abdicate the ring.”