In Elon Musk’s upcoming biography, it will be revealed that he and his on-again, off-again ex-girlfriend Grimes quietly had a third child, whom they named Techno Mechanicus. This brings his total number of children to ten.

The news came out in a Saturday review of Elon Musk, the soon-to-be-published biography of the founder of Space X. The review was published by The New York Times.

Walter Isaacson wrote the book, which took him two years to write and will come out on September 12. The author has written about Albert Einstein, Steve Jobs, Leonardo da Vinci, and Benjamin Franklin in the past.

Isaacson followed Musk, who is 52, around for two years to learn a lot about his life for his planned biography.

The ex-couple’s third child, whose existence had been kept secret until now, was mentioned barely in the long review.

“The musician Grimes is the mother of three of Musk’s children. Until now, no one knew about the third, Techno Mechanicus, who goes by the nickname Tau.” The review tells you.

We don’t know much else about this third child, like what gender it is, when it was born, or where it is now.

Musk started dating Grimes, who is 35, in 2018. They were together on and off for about three years. They also have a 3-year-old son named X-A-12 and a 1-year-old girl named Exa Dark Siderael.

Three days before, the Genesis singer wrote a tweet, which has since been deleted, begging Musk, “Let me see my son.” She didn’t say the child’s name when she talked about him or her.

The CEO of Tesla has a total of ten children. Some of them are with Justine Wilson, Grimes, and Shivon Zilis, who are among his current and former partners.