Elon Musk's father has revealed he has a "secret" second child with his 35-year-old stepdaughter.

Errol Musk, 76, who is an engineer in South Africa, had a child, Elliot Rush, now 5, with Jana Bezuidenhout in 2017.

Bezuidenhout is the daughter of Heide Bezuidenhuot, Errol's second wife.

Jana was 4 when Errol became her stepfather. Errol and Heide were married for 18 years and had two children together.

Errol married Heide after separating from Maye Musk, Elon Musk's mother, in 1979.

The senior Musk told The Sun that a second baby born in 2019 was unplanned.

When asked by The Sun what Jana's stepsisters thought about the relationship, Errol said they found it "creepy".

"They still don't like it. They still feel a bit creepy about it, because she's their sister. Their half-sister," Errol told the Sun.

Errol now has a total of seven children, including Tesla CEO Elon Musk.

Meanwhile, last month it was revealed Elon, the billionaire Tesla founder, had twins in November with Shivon Zilis, a director at one of his companies.

Musk has a known total of nine children. He also has two children with Claire Boucher, better known as the musician Grimes, and five - a set of twins and a set of triplets - with his first wife, the writer Justine Musk.

Musk had previously expressed his feelings about having children on Twitter, posting: "Doing my best to help the underpopulation crisis. A collapsing birth rate is the biggest danger civilisation faces by far."