That’s according to Walter Isaacson’s biography Elon Musk, which published today. The revelation is a rare personal detail in a book that delves deeply into Musk’s cutthroat approach to business but steers clear of details about his 10 children, including the fact that a 10th had just been born during the pandemic. 

“When X was born, Musk took a picture of Grimes’ having a C-section and sent it around to friends and family, including her father and brothers,” Isaacson writes, noting that Grimes was “understandably horrified” and rushed to delete the photo. 

Grimes’ reaction took Musk by surprise, according to the pop star and performance artist who would go on to have two more children with him, one of whom was disclosed to the world in the new biography. 

“He was just clueless about why I’d be upset,” Grimes told Isaacson, attributing the flop to his neurodivergence. “It was his Asperger’s coming out in full,” she said.

The son, who became known as X, was born in May 2020. He would soon accompany his dad “everywhere,” Isaacson wrote. X “would sit on his father’s lap during long meetings, ride on his shoulders around the Tesla and SpaceX factories, wander precariously through solar roof installation sites” and watch rocket launches with his dad. According to Isaacson, the launch videos were so frequent that X learned to count down from 10 before he learned to count sequentially.  

Musk and Grimes would go on to have two more children together, a son named Techno Mechanicus, nicknamed Tau, and a daughter named Exa Dark Sideræl, nicknamed Y.

According to Isaacson, the couple broke up before their second child was born, figuring “it would be easier to be co-parents if they weren’t involved romantically,” but the breakup didn’t last, and the relationship between the two became an elaborate on-again, off-again affair. 

The episode with Grimes illustrates the difficulty Musk has had in his personal life, with former wives whom Isaacson interviewed complaining about Musk’s obsessions with work or his lack of empathy. Justine Wilson, Musk’s first wife, told Isaacson that Musk was “a great man in a lot of ways…but it’s that lack of empathy that gives me pause.” 

According to the book, a lack of empathy is core to Musk’s life philosophy—one of a series of “life lessons” from playing his favorite video game, Polytopia, with the first rule being “empathy is not an asset.” 

Musk has admitted to giving employees what he calls “hardcore” feedback—a favorite word of his that he has used for years at Tesla and Twitter—saying “I try to criticize the action, not the person.” Examples of this on display in the book: Musk instructing a young financial analyst that “if you don’t step on toes, I will fire you,” and regular feedback about ideas as “stupid” and people as “idiots.” This approach has turned off many workers, with Tesla being sued last year for fostering a “toxic” culture, but it’s also drawn many to Musk’s side. Isaacson even quotes several workers who quit SpaceX, tired of the unrelenting pace, only to find themselves bored and ask for their jobs back. 

Even Wilson, who told Isaacson she wishes Musk had shared more of his inner life with her when they were married, conceded that his aloofness was likely an asset in running his companies.

“The strong will and emotional distance that makes him difficult as a husband…may be reasons for his success in running a business,” she told Isaacson.