Elon Musk, the billionaire CEO of Tesla, has welcomed a third child with his former partner, Grimes, according to a forthcoming biography by Walter Isaacson. The child, named Techno Mechanius but affectionately known as Tau, has until now been kept a closely guarded secret.

Details about the child's age are undisclosed. Musk, 52, and the Canadian electro music star, Claire Boucher, who goes by the stage name Grimes, had an on-and-off relationship between 2018 and 2022.

They are already parents to two other children: X Æ A-Xii, known as X, born in 2020, and Exa Dark Sideræl Musk, nicknamed Y, born in March of this year. However, the couple reportedly separated last year. Excerpts from Isaacson's biography have sparked controversy, revealing Musk's involvement in the Russia-Ukraine war.

It was disclosed that Musk ordered SpaceX engineers to cut off Ukrainian access to Starlink satellites near the Crimean coast to prevent a surprise drone attack on Russian warships. Musk was said to fear the attack on occupied Crimea could be a "mini-Pearl Harbor." However, he took to Twitter to clarify that the Starlink regions in question were not activated and SpaceX did not deactivate anything.

Isaacson's biography also delves into Musk's personal life, including his relationship with Neuralink executive Shivon Zilis. On September 6, Isaacson shared images of Musk with Zilis and their twin children, who were born in November 2021. The release of these pictures prompted Grimes to express her frustration on Twitter, claiming she had never been allowed to see a photo of her children until that moment.

The biography aims to provide an inside look into Musk's life and the driving forces behind his innovations and accomplishments. Isaacson spent two years shadowing Musk, attending his meetings, touring his factories, and conducting extensive interviews with him, his family, friends, coworkers, and adversaries. The book, titled "Elon Musk," is set to be released on September 12.