Grimes and Elon Musk are now the parents of two.
In Vanity Fair's April 2022 cover story published Thursday, the singer said she and Musk welcomed their second child, who was born in December 2021, via surrogate.
The two also have a 22-month-old son, X Æ A-12.
The name of their second child is Exa Dark Sideræl, nicknamed "Y," Grimes told the magazine.
Exa refers to a supercomputing term exaFLOPS and Dark represented "the unknown," according to Grimes.
"People fear it but truly it’s the absence of photons," she said. "Dark matter is the beautiful mystery of our universe."
Sideræl — pronounced “sigh-deer-ee-el" — represents "the true time of the universe, star time, deep space time, not our relative earth time,” the 33-year-old singer said, adding that it was also a nod to her favorite "Lord of the Rings" character, Galadriel, who "chooses to abdicate the ring."
In the VF interview, Grimes also revealed she and Musk got back together after reportedly calling it quits late last year.
“There’s no real word for it,” she said. “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.”
The two want to have more children.
"We've always wanted at least three or four," she said.
Representatives for Grimes and Musk did not immediately respond to NBC News' request for comment.
