Elon Musk and Grimes Used IVF to Conceive Their First Baby, Son X Æ A-Xii, New Book Reveals

Elon Musk and Grimes are sharing new details about their journey as parents.

In his new biography on the SpaceX founder, titled Elon Musk, Walter Isaacson profiles the tech entrepreneur and discusses his 11 kids, including his three with ex Grimes, 35. While writing about the couple's first child, son X Æ A-Xii "X," Isaacson revealed that the couple used in vitro fertilization (IVF) to help them conceive.

"Musk and Grimes, who conceived [X] through in vitro fertilization, had planned to have a girl, but the fertilized egg that got implanted, as they were preparing to go to Burning Man in 2019, turned out to be male," Isaacson wrote.

He went on to reveal that Grimes and Musk, 52, struggled with choosing a name for a boy until the last second. "Up until the day he was born, they were having trouble settling on names for a boy," the author shared.

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Musk and Grimes share three kids together — sons X, 3, and Techno Mechanicus, and daughter Exa Dark Sideræl, 22 months, whom they call Y.

Isaacson's biography was the first time the public found out about the couple's third baby, which remained a secret until publication. Representatives for both Musk and Grimes did not immediately respond to PEOPLE's request for comment at the time.

In the same biography, Grimes shared more details about giving birth to X, revealing that Musk had snapped a photo of the singer as she was having a C-section and sent it around to their friends and family, including Grimes' father and brothers.

"He was just clueless about why I'd be upset," Grimes told Isaacson.

In a March 2022 Vanity Fair interview revealing Exa Dark’s birth, Grimes admitted that the former couple wanted more babies, telling the outlet, "We've always wanted at least three or four."

But the day the article was released, the "Genesis" singer tweeted that the couple had broken up again.

In addition to the three kids he shares with Grimes, Musk is also a father to the six children he shares with his ex-wife, Canadian author Justine Wilson. He is also dad to 22-month-old twins Strider and Azure with Neuralink exec Shivon Zilis.