Grimes has welcomed her second child with Elon Musk. The 33-year-old musician, whose real name is Claire Ellis Boucher, shared the news in a new Vanity Fair cover story.
During the interview, Grimes is at first hesitant to discuss the details of her family, saying, "I'm not at liberty to speak on these things. Whatever's going on with family things, I feel like The kids need to be out of it, and X is out now."
However, she then shares that she and 50-year-old Musk secretly welcomed a daughter they call Y through a surrogate in December.
"Her full name is AXA Dark Siderel Musk," Grimes tells the magazine.
As for the meaning behind the unique moniker, Grimes shares that the term exa supercomputing refers to exaflops (the ability to perform 1 quintillion floating-point operations per second), while dark represents the "unknown".
"People are afraid of it but it's really the absence of photons," Grimes says. "Dark matter is the beautiful mystery of our universe."
As for the siderail - pronounced ah-deer-ee-l - Grimes describes it as a "greater elf" spelling of "sidereal", meaning "the true time of the universe, star time, deep space time, not our relative Earth time." It's also a nod to Grimes' favorite Lord of the Rings character, Galadriel.
Despite welcoming a second child together, Grimes remains unclear about her romantic status with Musk.
"There's no real word for it," she says. "I'd probably refer to him as my boyfriend, but we're very fluid. We live in different houses. We're best friends. We see each other all the time... we just have our say It's going on, and I don't expect others to understand it."
She says their relationship is "the best ever", adding that they plan to have more children in the future.
"We always want at least three or four," she says.
As for his first child, Grimes says Musk has high hopes for a nearly 2-year-old.
"I think E is really seeing him as a shelter and bringing him into everything and stuff. X is out there," she says. "His position is like this."