Shivon Zilis, a Neuralink executive and the mother of four of Elon Musk’s children, took the stand on Wednesday as one of the most highly anticipated witnesses in Musk’s case against OpenAI. The ChatGPT maker has argued that, while Zilis worked with OpenAI between 2016 and 2023, she was also involved in a secret relationship with Musk, acting as an informant for him.

Musk’s case against OpenAI alleges that the company’s CEO, Sam Altman, and president, Greg Brockman, co-founders of the company with Musk, broke a founding agreement when they restructured it from a non-profit to a for-profit enterprise. The Tesla CEO accuses Altman and Brockman of unjustly enriching themselves and wants both removed from their positions at the startup, one of the most valuable in the world. He is also seeking the undoing of the for-profit restructuring and $134bn in damages to be redistributed to OpenAI’s non-profit arm.

OpenAI rejects all of Musk’s allegations and over the course of the trial, now in its second week, has tried to prove that he was always onboard with the intentions to shift to a for-profit structure. The company’s lawyers have argued that Musk was essentially a sore loser who left the company in 2018 after a failed bid for control and was seeking vengeance due to OpenAI’s success.

Zilis has become an important figure in the case, as she served as a link between Musk and OpenAI’s board, which she served on from 2020 to 2023. In pre-trial filings, OpenAI’s lawyers questioned the exact nature of Zilis’s relationship with Musk and presented communications to suggest she was working as an inside source for him after he left the company. She met Musk through her work at OpenAI.

“Do you prefer I stay close and friendly to OpenAI to keep info flowing or begin to disassociate? Trust game is about to get tricky so any guidance on how to do right by you is appreciated,” Zilis texted Musk in 2018, according to court filings.

“Close and friendly, but we are going to actively try to move three or four people from OpenAI to Tesla. More than that will join over time, but we won’t actively recruit them,” Musk responded.

Meanwhile, Zilis remained on good terms with OpenAI’s leadership. A 2023 text from Altman to Zilis suggests that he was seeking her advice on how to influence Musk – asking her: “BTW, good idea for me to tweet something nice about Elon?”

Zilis, 40, took on a role as project director at Tesla in 2017, and when she joined OpenAI’s board she was its youngest member. She is now an executive at Musk’s brain-implant startup Neuralink. The extent of Zilis’s personal relationship with Musk wasn’t publicly known until 2022, when Business Insider reported that she had twins with Musk the year before.

The case has revealed additional information about Zilis and Musk’s relationship: the two became romantically involved around 2016, according to Zilis’s testimony, and she lives in a house in Austin where he sometimes stays when visiting their children. Zilis said that she decided to have children with Musk around the end of 2020 when he told her he would “be happy to make a donation”.

When Musk took the stand last week, he referred to Zilis as the mother of his children. He also testified that he lives with Zilis.

During Zilis’s testimony, she said that she first became enthralled with AI as a 13-year-old growing up in the suburbs of a town in Ontario, Canada. She said she read the book Age of Spiritual Machines by Ray Kurzweil, which is about AI merging with human consciousness.

“I read it 10 to 15 times and it never left me from there,” Zilis said. “AI is going to be the most influential thing humanity creates.”

Zilis said she went to college at Yale University and immediately after started working in the tech industry, first at IBM and eventually landing an adviser role at OpenAI in 2016. It was there that she met Musk, when he was standing outside the office one day talking to Altman. By mid-2017, Zilis had begun working for Musk at Tesla and Neuralink.

She said her job was to “go find the bottlenecks and go help solve them”. Zilis said she worked 80- to 100-hour weeks: “It was just bananas.”

Brockman was also questioned about Zilis and her role at the company when he testified earlier this week. He said Zilis was a friend of his, whom he met around 2012 or 2013, and that she later went to work for Musk.

Brockman said that after Musk left OpenAI in 2018, Zilis was “kind of our proxy Elon in some ways” and “very” involved in the restructuring of OpenAI into a for-profit entity. When Zilis gave birth to twins in 2021, Brockman said she didn’t say who the father was and he had no idea about her romantic relationship with Musk. Brockman testified that he found out about it in the news.

At the time, “she said that it was via IVF and that it was entirely platonic with Elon”, Brockman said.

Zilis testified that she has signed a confidentiality agreement with Musk to not disclose they had children together, but that, when she was contacted by Business Insider about the story, she told OpenAI immediately. “First call was to my dad,” Zilis said. “The next call was to Sam Altman.”

OpenAI’s board voted to let her stay on, but she eventually left when Musk started his own competing AI company, xAI, in 2023. Since then, Zilis and Musk have been seen holding hands and attending events together, including dinners with Donald Trump at the White House and Mar-a-Lago.