Although the status of Elon Musk and Grimes’ relationship has been unclear since the tech billionaire said they were “semi-separated” in September, they are apparently close enough to have a second child together.The 33-year-old singer revealed to Vanity Fair that she and Musk had a baby girl in December 2021 via a surrogate. The baby’s full name is Exa Dark Sideræl, but her parents call her simply Y. The couple’s first child, a boy, is named X AE A-Xii, and goes by X.Grimes said their new baby’s name references the supercomputing term exaFLOPS, while “Dark” represents “the unknown,” adding, “Dark matter is the beautiful mystery of our universe.” Meanwhile, Sideræl — which is pronounced “sigh-deer-ee-el” — refers to “the true time of the universe, star time, deep space time, not our relative earth time.” It’s also a nod to Galadriel, a character from ”Lord of the Rings.”But, Grimes noted, Exa wasn’t her first choice. She told Vanity Fair that she lobbied to name her daughter Odysseus Musk because “a girl named Odysseus is my dream.”Although Musk appeared to announce their separation last fall, Grimes told Vanity Fair that she and Musk are indeed together, though they don’t use typical labels. “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.”More kids could be on the horizon for the pair. Grimes said she and Musk have talked about having three or four kids.