According to The New York Times’ review of Musk’s biography, which was written by journalist Walter Isaason and set to be released on Sept. 12, Musk, 52, and Grimes, 35 — whose real name is Claire Boucher — welcomed a third child, a son named Techno Mechanicus, who also goes by “Tau."
It is unclear if the Space X founder's forthcoming biography contains more details about the infant, including when or where he was born.
Musk and Grimes welcomed son X Æ A-12, whose name was later changed to X Æ A-Xii and is nicknamed “X,” on May 4, 2020.
They then welcomed a daughter born via surrogate in December 2021, named Exa Dark Sideræl, who is nicknamed “Y," three months after they publicly broke up after three years together.
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.
Alongside 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.
Musk had his first son, Nevada Alexander, with Wilson in 2002, but at 10 weeks old he died from sudden infant death syndrome (SIDS).
Wilson then gave birth to triplets named Kai, Saxon, and Damian in 2006, two years after having their twins.
Musk later secretly welcomed another set of twins, son Strider and daughter Azure, with Shivon Zilis in November 2021, according to court documents published by Insider on July 6. The twins were born in Austin, Texas — just weeks before he and Grimes welcomed their daughter together.
Grimes opened up about co-parenting with Musk in an interview with Wired last month, saying that they are in the process of figuring out what their children's educational journeys will look like.
"I really care about having a very good relationship with my kids. I think I understand how to be a good parent to them. Both enforcing discipline and being their friend," she said. "Who knows, maybe they’ll resent me and reject family culture, but I feel like they will not."