OAKLAND, Calif. — Shivon Zilis, a longtime adviser to tech billionaire Elon Musk who also is the mother of four of his children, took the witness stand Wednesday in a trial that has given a rare glimpse into some of Silicon Valley’s complicated relationships.

Zilis testified on the sixth day of the trial. Musk, a co-founder of artificial intelligence startup OpenAI, is suing two of his co-founders, OpenAI CEO Sam Altman and President Greg Brockman, alleging that they are enriching themselves from what he says was supposed to remain a charitable endeavor.

Zilis fits into the case in multiple ways. She not only worked at OpenAI beginning in 2016 but also served on its board of directors for several years, operating as a kind of bridge between Musk and the firm’s other co-founders even after they had fallen out. She left the OpenAI board in 2023, after Musk started a competitor AI company, xAI, and has also worked at Musk’s brain science startup, Neuralink, and at Tesla, where Musk is CEO.

During initial questioning from a Musk lawyer, Zilis was asked about both her board service and her relationship with Musk.

She described a complicated relationship with Musk. It began, she said, with “a one-off” at a corporate off-site event. Later, after she decided to have children as a single mother, she said Musk “offered to make a donation” as a platonic sperm donor. And later still, she said, their relationship evolved. She said they now have a romantic partnership.

She said, though, that their relationship did not affect her decisions as an OpenAI board member.

“I had an allegiance to the best outcome, AI for humanity,” she said.

Zilis faced many questions on the stand about her loyalties. Asked by Musk lawyer Jennifer Schubert whether it was her job “to funnel information to Elon,” she responded, “Funnel? Absolutely not.”

Schubert also asked about a message Zilis sent to Musk saying the “trust game is about to get tricky” regarding her interactions with other OpenAI board members. Zilis testified that she was not being duplicitous with Altman and Brockman.

“I would have preferred it if I’d written ‘trust framework,’” rather than “trust game,” she testified. She said that back in 2017 the OpenAI co-founders were going through a “weird half-breakup” and “I think I wanted to figure out how to navigate, if I was still going to be a facilitation or a bridge.”

At an earlier stage in the lawsuit in 2024, Zilis was a plaintiff alongside Musk in the claims against Altman and Brockman. She dropped out of the case as a plaintiff last year.

Though she keeps a low profile in some ways, including rarely granting media interviews, Zilis is an important piece of Musk’s public image. She has 276,000 followers on X, the social media app that Musk owns, and regularly posts there about technology and family.

Last year, Zilis announced that she and Musk had welcomed a fourth child. Musk has fathered 14 known children.

Zilis has sometimes appeared alongside Musk in public. In February, she was photographed holding Musk’s hand as they arrived at Mar-a-Lago, President Donald Trump’s Florida club. And last year, when Musk was serving in the Trump administration, Zilis joined Musk for a meeting with India Prime Minister Narendra Modi.

Brockman testified Tuesday that he and Zilis had been friends at least since 2013. They later worked together at OpenAI and served together on the firm’s board. He said that Zilis told him in 2021 about being pregnant with twins but did not tell him who the father was, and that he learned who it was only through media reports. He said they then spoke about it.

“She said it was via IVF and that it was entirely platonic with Elon,” Brockman said on the stand.

Zilis was on the OpenAI board at the time, and Brockman testified that “many board members” wanted to remove her from the board because of her relationship with Musk.

“We actually had a board vote and decided to let her stay. We trusted her to keep the Elon conflict under control,” Brockman said.

On the stand Wednesday, Zilis said she informed the OpenAI board about her relationship with Musk only after a news outlet, Business Insider, found out about the relationship and told her they planned to publish a story.

She and Musk initially “had agreed on complete confidentiality” about his donation of sperm, she said, due to security concerns. She said the security around Musk is a burden.

“If he was indeed just a donor, it didn’t seem fair to put that burden on them,” she said.

Zilis peppered her speech with unusual phrases and occasional sarcasm. At one point, when she did not recall a detail, she testified, “It’s not in my neurons.” At another time, she said she had been working on “seven zillion” projects and added, “It’s a precise, technical term.”