• Walter Isaacson shared a peek into Elon Musk's relationship with Shivon Zilis, one of the mothers of his children.
  • Zilis is a director at Musk's brain chip company who quietly had a set of twins with the billionaire.
  • Isaacson said he went to Zilis' house earlier this year to discuss the threat of AI with Musk.

Author Walter Isaacson gave a peek into Elon Musk's relationship with Shivon Zilis, a Neuralink director and the mother of two of Musk's children, on Wednesday in an excerpt from his forthcoming biography on the Tesla CEO.

The biographer, who has been shadowing Musk for about three years, posted a picture of Musk and Zilis with their two children in tow on X, formerly known as Twitter. In the photo, the twins — who were 16 months old at the time — sit on the laps of Zilis and Musk.

Elon Musk pictured with Shivon Zilis and the twins they had together.
Elon Musk pictured with Neuralink director Shivon Zilis. Insider first reported that Musk had quietly fathered twins with Zilis in November 2021.
Walter Isaacson

Last year, Insider first revealed that Musk had quietly fathered a set of twins with Zilis in November 2021 and Reuters later reported that she had told her colleagues at Neuralink that they had conceived the children via in vitro fertilization and did not have a romantic relationship. Musk has nine known living children.

Little has been reported on Musk's relationship with Zilis, who joined Musk's brain chip company Neuralink in 2017 as the director of operations and special projects, according to her LinkedIn profile. She was also an advisor and later a board member at OpenAI from 2016 up until March when she stepped down from the AI company's board of directors, The Information first reported.

Watch: 5 ways Elon Musk shook up Twitter as CEO

Isaacson said the photo was taken when Musk invited him to meet up in Austin, Texas for a chat at Zilis' house.

"This past March, Musk texted me, 'There are a few important things I would like to talk to you about. Can only be done in person,'" Isaacson wrote in an excerpt from his biography on Musk that was posted in TIME Magazine. "He said we should leave our phones in the house while we sat outside, because, he said, someone could use them to monitor our conversation. But he later agreed that I could use what he said about AI in my book."

The biographer said Musk walked him and Zilis through his concerns about AI, including that AI's rapid development was on a collision course with a "leveling off" in human intelligence that Musk attributed to lower human birth rates.

"For a moment I was struck by the oddness of the scene," Isaacson wrote of the encounter. "We were sitting on a suburban patio by a tranquil backyard swimming pool on a sunny spring day, with two bright-eyed twins learning to toddle, as Musk somberly speculated about the window of opportunity for building a sustainable human colony on Mars before an AI apocalypse destroyed earthly civilization."

Ultimately, Isaacson said the conversation was the beginning of Musk's latest company x.AI, which he later officially unveiled in July. The billionaire has said the goal of the company is to find "the true nature of the universe." It is set to go head-to-head with other AI powerhouses like OpenAI and Google.

Read the full excerpt on TIME's website.