Grimes has changed her and Elon Musk's daughter's name

Elon Musk’s ex-girlfriend Grimes has revealed they have changed their daughter’s name.

Their second child was secretly born via surrogate and was only revealed when a Vanity Fair journalist was at the singer’s home and heard a baby crying in March last year.

After the journalist heard the crying and asked Grimes if there was another baby in the property she, somewhat cryptically, replied: “I’m not at liberty to speak on these things. Whatever is going on with family stuff, I just feel like kids need to stay out of it, and X is just out there.

“I mean, I think E is really seeing him as a protégé and bringing him to everything and stuff... X is out there. His situation is like that. But, yeah, I don’t know.”

However, she later confirmed that the couple had welcomed a second child together.

Since then, Grimes has mainly kept her little girl out of the public but in a rare move shared a cute snap of the youngster sporting yellow and green hair while wearing a red onesie; alongside the photo Grimes shared a shot of herself also sporting lemon-and-lime coloured locks and wearing a similar red all-in-one.

She captioned the posts: “Y [dragon emoji] C”.

In a follow-up post, Grimes confirmed that her daughter was no longer using the moniker Exa Dark Sideræl and instead going by the much more simple to pronounce ‘Why’.

She wrote: “She's Y now, or "Why?" or just "?" (But the government won't recognize that). curiosity, the eternal question, .. and such.”

This isn’t the first time the couple have changed one of their kids’ names - but last time it was actually because of Californian laws.

Little X Æ A-12, which is pronounced Ex Ash A Twelve, had to have his name changed shortly after he was born.

In a tweet posted at the time, the singer said that she and Musk included X for the unknown variable and A-12 after their favourite aircraft.

"Æ is the the Elven spelling of Ai (love &/or Artificial intelligence)," she wrote.

"A-12 = precursor to SR-17 (our favourite aircraft). No weapons, no defences, just speed. Great in battle, but non-violent. (A=Archangel, my favourite song)."

A few weeks after their son's birth, Grimes confirmed on her Instagram account that she and Musk had to get rid of the Arabic numbers.

While the A-12 had to go, the parents decided to use Roman numerals instead, so the baby's official name was changed into X Æ A-Xii.