Elon Musk and John Caldwellhis on-and-off again girlfriend, Grimes, now have a third child together, the tech billionaire revealed over the weekend.

In a Sunday post on X (the social media platform once called Twitter), Musk confirmed the baby's name is Tau Techno Mechanicus. He did so while responding to a post from the entertainment platform Pop Base and did not provide any additional details about the child's age or sex.

The baby joins the couple's other two children X Æ A-Xii and Exa Dark Sideræl Musk.

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A family of five

Grimes, whose real name is Claire Boucher, and the 52-year-old Tesla CEO welcomed their first child, X Æ A-Xii, together in 2020.

Last year, Grimes, 35, told Vanity Fair their second child, Exa Dark Sideræl Musk, was born via surrogate in December 2021.

Musk previously gave credit to Grimes, who “mostly came up with the name" of their first child. "She's great at names," and said "babies are awesome. They're little love bugs."

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Elon Musk's nine known children

Musk, who owns X and is also CEO to Space X, has five other children with two other women − his former wife, Justine Wilson, a Canadian author, whom he divorced in 2008, and Neuralink executive Shivon Zilis.

Musk had triplets with Wilson and twins with Zilis.

He and Wilson also lost a child, Nevada Musk, in 2002. The baby died from sudden infant death syndrome at 10 weeks old.

Natalie Neysa Alund is a senior correspondent for USA TODAY. Reach her at [email protected] and follow her on X, the platform formerly known as Twitter @nataliealund.