Elon Musk and Grimes' Second Child Has a Unique Name Just Like Brother X AE A-Xii

Grimes and Elon Musk have a knack for giving their children truly unique names. The singer confirmed Thursday, March 10 that she and the Tesla CEO welcomed their second child in December 2021 via surrogate, and they gifted their baby daughter with the moniker Exa Dark Sideræl. Little Y, as the couple has adorably nicknamed her, joins the couple's older son X Æ A-12, who they welcomed in May 2020.

Grimes confirmed the birth to Vanity Fair in a cover story for the magazine's April 2022 issue, the newly-minted mom of two also dishing some details about her daughter's name and the special meaning behind it. According to Grimes, her daughter's first name, Exa, refers to the supercomputing term exaFLOPS. Her middle name, Dark, meanwhile, represents "the unknown." Grimes explained, "people fear it but truly it's the absence of photons. Dark matter is the beautiful mystery of our universe."

The third part of Y's name is Sideræl, which is pronounced sigh-deer-ee-el, according to the new mom and Vanity Fair. Grimes called the name "a more elven" spelling of sidereal, "the true time of the universe, star time, deep space time, not our relative earth time." However, there is a little more significance to the moniker as well, as Sideræl is also a nod to Grimes' favorite Lord of the Rings character, the powerful Galadriel, who "chooses to abdicate the ring."

Grimes revealed that the name wasn't initially at the top of her list. In fact, the singer was actually "fighting" for Odysseus Musk. Grimes revealed that "a girl named Odysseus is my dream." However, the couple ultimately decided on Exa Dark Sideræl. The name will likely cause some chatter on social media, and Grimes shared that she is prepared for Y to one day dislike her name. Should that happen, Grimes said she will happily support her daughter in changing her name and will even be the first in line to offer up suggestions.

The little one's unique name comes as little surprise given the couple's oldest child's name, X Æ A-12, whom they sweetly call X. Shortly after confirming X's birth, the couple revealed that the A-12 portion was in reference to the couple's "favorite aircraft, the Lockheed A-12 reconnaissance aircraft built by the U.S. Central Intelligence Agency.

Y's arrival comes after Grimes and Musk split up in September 2021 after three years together. The singer told Vanity Fair she and Musk are back together, explaining, "there's no real word for it. I would probably refer to him as my boyfriend, but we're very fluid. We live in separate houses. We're best friends. We see each other all the time."