Elon Musk and Grimes have welcomed a new baby to their brood, via surrogate. And like her big brother, Grimes’ first child X Æ A-Xii, the new addition has an…interesting name: Exa Dark Sideræl [sigh-DEER-ee-al] Musk. 

For the record, they normally just refer to her as Y, Grimes says in a wife-ranging feature piece in Vanity Fair — and their son usually goes by X. 

The new baby’s name was born of a multitude of references, Grimes explains, with “Exa” as in exaflops, or the ability for a computer to perform a quintillion operations a second. “Dark” represents “the unknown…and also the absence of photons making up dark matter, “the beautiful mystery of our universe,” 

Sideræl, Grimes describes as “a more elven” spelling of “sidereal,” which Grimes calls, “the true time of the universe, star time, deep space time, not our relative earth time,” while also being a nod to the Elven queen Galadriel from The Lord of the Rings.  

The coupling between the avant-garde musician and the billionaire creator of Tesla Motors and SpaceX was widely reported to have been over, but as she tells the magazine, “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.”

Grimes says of their relationship, “This is the best it’s ever been,” and they plan to have “at least three or four” children together — so plan on some more interesting names in the future. 

That said, she tweeted today, “Me and E have broken up *again* since the writing of this article haha, but he’s my best friend and the love of my life.”

Elon Musk already has six other children from previous relationships — Nevada, Xavier, Damian, Griffin, Kai, and Saxon. 

We’re pretty sure he can afford the large family.