Pop singer Grimes and entrepreneur Elon Musk have welcomed a second child together.

The daughter, named Exa Dark Sideræl Musk, abbreviated "Y", was born in December with the help of a surrogate mother, Grimes said in an interview with Vanity Fair magazine.

The Canadian musician, whose real name is Claire Elise Boucher, and Musk, 50, the founder of companies like SpaceX and Tesla, have been parents to a boy named "X Æ A-Xii", abbreviated "X", since 2020.

Musk also has five children with ex-wife Justine Wilson.

Musk, Grimes and their two children now live in Austin, Texas.

There is "no name" for their relationship status, Grimes said.

"I would probably call him my boyfriend, but we're very fluid there.

We live in different houses.

We are best friends.

We see each other all the time.

We have our own thing and I don't expect other people to understand that." They are happy and also plan to have more children.

"We've always wanted at least three or four."