The 32-year-old singer had her first child on Monday. Musk, 48, confirmed the big news on Twitter, saying "Mom and baby all good."
Musk first broke the news when a Twitter user asked him for an update on the baby.
Grimes sparked pregnancy rumors in January when she posted a nude photo of herself on Instagram. A baby bump and fetus photoshopped over her stomach were clearly visible.
Fans didn't have to speculate for long. Grimes later took to Instagram to express her woes surrounding her pregnancy.
"This whole thing has been a bit of an ordeal," the singer wrote in an Instagram post. "What were yalls experience w this stuff like? I feel like I was woefully ill prepared cuz I dunno if pregnancy is as visible or discussed as it should be. I just didn’t rly understand what I was getting into. It’s been good too, but it makes working a lot harder."
The Canadian singer joked that she thinks her kid will be a night owl , saying "he doesn't move during the day, only at night."
Grimes, whose real name is Claire Boucher, has been with Elon Musk for two years.
This is Musk's sixth child. He has five sons -- a set of twins and a set of triplets -- from a previous marriage.
The SpaceX mastermind announced his new son's name is something a little out of the box: X Æ A-12 Musk.