Elon Musk fathered twins with a top executive at his artificial intelligence startup Neuralink, court documents show.
In April, Mr Musk and Shivon Zilis filed a petition for the twins to "have their father's last name" and their mother's last name as part of their middle name, according to court documents cited by Business Insider.
A Texas judge approved the petition a month later, the report said.
It brings the total number of children Mr Musk has to nine.
He shares two children with Canadian singer Grimes and five others with his ex-wife Justine Wilson.
Ms Zilis reportedly gave birth to the twins in November 2021, weeks before Mr Musk and Grimes welcomed their second child via surrogate.
The billionaire said he and the singer were "semi-separated," according to a report by Page Six in September last year.
According to her LinkedIn, Ms Zilis, 36, is director of operations and special projects at Neuralink.
She started working at the company in May 2017, the same month she was named a project director in artificial intelligence at Tesla, where she worked until 2019.
She is also a board member at artificial-research firm OpenAI, which was co-founded by Mr Musk, according to her LinkedIn profile.
The Business Insider report said Ms Zillis has "been floated" to run Twitter after Mr Musk's $44bn (£36.8bn) acquisition of the social media giant, which has recently been put on hold over his concerns about bots on the platform.
It comes after Mr Musk's transgender daughter applied to legally change her name because she no longer wants to "live with or wish to be related to my biological father in any way, shape or form".