Elon Musk and Grimes Welcomed a Baby Girl, Nicknamed ‘Y,’ in December

Tesla and SpaceX CEO Elon Musk and singer Grimes have welcomed a baby girl.

Exa Dark Sideræl Musk was born in December via surrogate. She joins big brother X Æ A-12, which is pronounced “X A.I. Archangel,” who was born in May 2020. For short, the girl is called “Y,” and the boy is called “X.”

The couple had kept the baby a secret until it was revealed Thursday in Vanity Fair cover story on Grimes. According to the story, Exa refers to a the supercomputing term exaFLOPS, Dark refers to “the unknown,” and Sideræl (pronounced “sigh-deer-ee-el” is “a more elven” spelling of sidereal, which she described as “the true time of the universe, star time, deep space time, not our relative earth time.”

This is the second child for Grimes, who was first romantically linked to Musk in 2018. He has five sons from a previous marriage. (His first son, Nevada, died of SIDS at 10 weeks old in 2002.)

Grimes told VF that she had a difficult first pregnancy, particularly in the last couple months. “He was pressing on my nerves, so I kept collapsing,” she said. “I took a few steps and collapsed. It was kind of scary, because you don’t want to fall a lot when you’re eight months pregnant. So I would just crawl to the bathroom and crawl back or whatever.” She also hemorrhaged and was afraid she was going to die.

Though the couple split up in September, Grimes confirmed they are back together. “There’s no real word for it,” she told VF. “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. … We just have our own thing going on, and I don’t expect other people to understand it.”

As for their daughter, the VF writer learned of her existence when the baby began crying in an upstairs room of Grimes’ house, where the interview was being conducted. Asked if she had a baby, Grimes first said: “I’m not at liberty to speak on these things. Whatever is going on with family stuff, I just feel like kids need to stay out of it, and X is just out there. I mean, I think E is really seeing him as a protégé and bringing him to everything and stuff.… X is out there. His situation is like that. But, yeah, I don’t know.”

After realizing she couldn’t deny the baby’s existence, once it began crying even more, Grimes laughed and admitted the truth: “She’s a little colicky too. I don’t know. I don’t know what I was thinking.”