It's probably safe to assume that you're aware of Musk and Grimes first child, X Æ A-12, so it's no surprise that their new baby girl, is called Exa Dark Sideræl Musk.
Musk and Grimes kept the baby, who was born via surrogate mother, very close to their chests. In fact, the news of the baby came to light during an interview with Vanity Fair, when the interviewer heard a baby crying.
Grimes tried to keep talking and not mention anything about the baby upstairs, but when the crying continued, admitted that the baby is in fact her and Musk's daughter.
The pair nicknamed X Æ A-12 "X", and so it's fitting that they've nicknamed their baby girl "Y".
Wonder when baby "Z" will be a thing.