Shivon Zilis, the mother of four of Elon Musk ’s children, revealed in court Wednesday personal details about her complicated and once-secret relationship with the tech billionaire , providing a rare glimpse into their private life during a high-profile legal battle over artificial intelligence.

Zilis, who is also a longtime adviser to Musk, took the witness stand on the sixth day of his lawsuit against fellow OpenAI co-founders Sam Altman and Greg Brockman. Musk alleges the executives abandoned OpenAI’s original nonprofit mission in pursuit of profit and personal gain.

The 40-year-old revealed that sometime after she joined OpenAI in 2016, she had a romantic “one-off” with Musk.…