Elon Musk Speaks Out After Welcoming Twins: 'Doing My Best to Help the Underpopulation Crisis'

Elon Musk is speaking out after a report this week revealed that he fathered twins with Neuralink executive Shivon Zilis last November.

On Thursday, one day after Insider published court documents that revealed Musk and Zilis secretly welcomed twins together, the Tesla CEO, 51, seemingly alluded to the baby news in a tweet about the "underpopulation crisis."

"Doing my best to help the underpopulation crisis. A collapsing birth rate is the biggest danger civilization faces by far," he wrote.

Adding in follow-up tweets, Elon wrote, "Mark my words, they are sadly true" and "I hope you have big families and congrats to those who already do!"

According to the court documents, the twins were born in Austin, Texas. The papers reveal that in April, Musk and Zilis –– who is the project director at his Neuralink company –– asked a Texan county court to change their babies' names so they would "have their father's last name and contain their mother's last name as part of their middle name."

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Kevin Mazur/MG22/Getty; Shivon Zilis/shivonzilis.com

RELATED: Elon Musk Had Twins Last Year with Exec Shivon Zilis Just Weeks Before His & Grimes' Baby Was Born

The twins' sexes were not made public and their names were redacted from the documents.

An Austin judge granted their request in May, per Insider.

For more on Elon Musk welcoming twins last year, listen below to our daily podcast PEOPLE Every Day.

A representative for Musk did not immediately respond to PEOPLE's request for comment. Zilis also did not immediately respond.

Pascal Le Segretain/Getty Elon Musk

The twins' arrival came just weeks before Musk and his former partner Grimes welcomed a baby girl via a surrogate in December, despite the pair splitting up in September. She revealed the birth of Exa Dark Sideræl, who they've nicknamed Y, in a cover story for Vanity Fair. They also share 2-year-old son X Æ A-12.

After welcoming the twins, Musk is now a father of 10. He shares 18-year-old twins Vivian Jenna Wilson and Griffin Musk, along with triplets Kai, Damian, and Sax Musk, who were born in 2006, with his first wife, Justine Wilson. The two had another son, Nevada Musk, who died at 10 weeks.

Theo Wargo/Getty Elon Musk with son X

Musk does not often discuss his own family, but he does have strong opinions on increasing the birth rate — stating that there are "not enough people" in the world at Wall Street Journal's annual CEO Council in December 2021.

"I think one of the biggest risks to civilization is the low birth rate and the rapidly declining birthrate," he said. "Please look at the numbers –– if people don't have more children, civilization is going to crumble, mark my words."