Elon Musk's dad has fathered a second child with his stepdaughter, who is 41 years his junior, he said in a new interview.

Errol Musk, 76, told The Sun Wednesday that he had a daughter with Jana Bezuidenhout, 35, in 2019.

The elder Musk and Bezuidenhout previously welcomed a son, Elliot Rush, who is now 5 years old.

Bezuidenhout's mother, Heide, and Musk were married for 18 years and share two children. Bezuidenhout was 4 years old when Musk became her stepfather.

Errol and Maye Musk were married from 1970 to 1979 and share three children: Elon, Kimbal, and Tosca.

Errol Musk told The Sun the child "wasn't planned," adding that he and Bezuidenhout lived together for roughly 18 months after the birth of their first child. They no longer live together but "have a lot of affection for each other," he said.

The elder Musk said his daughters were "shocked" by his relationship with Bezuidenhout. The New York Post reported that he had fathered a total of seven children.

"To them, it was their sister," he told The Sun. "They still feel a bit creepy about it, because she's their sister. Their half-sister."

Speaking with the tabloid, Musk echoed his son's views on population growth.

"The only thing we are on Earth for is to reproduce," he said. "If I could have another child I would. I can't see any reason not to."

Today, Errol and Elon Musk are estranged.

Insider reported earlier this month that Elon Musk quietly had twins in November with one of his top Neuralink executives, Shivon Zilis. That means he has nine known children.

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

The tech billionaire has repeatedly expressed concern about falling birth rates over the years. Last year, he tweeted that "civilization is going to crumble" if people don't have more children.

Experts say declining birth rates don't have to spell disaster if governments and corporate leaders take the right steps to adjust to a world with fewer people.