According to a media report, Elon Musk and Shivon Zilis have been parents of twins since November.
Musk and Zilis filed a request in April to have the children's names changed to "take their father's last name," Business Insider reported Wednesday, citing court documents.
The court agreed in May.
Shivon Zilis is a 36-year-old Canadian who works as a director at Musk's company, Neuralink.
The relationship becoming known through the name change could be problematic for the technology entrepreneur Musk.
Most US companies the size of Tesla and SpaceX prohibit romantic relationships across two hierarchical levels.
Zilis is also being considered as one of the people Musk could hire to run Twitter following his $44 billion acquisition, the report said.
Her career includes positions at Neuralink, Tesla and OpenAI, citing her now-deactivated LinkedIn profile.
All three companies have close ties to Musk, who founded Neuralink, co-founded OpenAI, and took over as CEO of Tesla in 2008.
Musk and Zilis did not immediately respond to a Reuters request for comment.
The news of the twins' birth in November brings Musk's total number of children to nine.
Musk and Canadian singer Grimes welcomed their second child via surrogate in December.
Musk has five more children with his ex-wife, Canadian author Justine Wilson.