Grimes has confirmed that she has changed the name of her baby with Elon Musk to comply with California state law.
Grimes confirms she and Elon Musk have changed their baby’s unusual name
Musk has previously announced his son was called X Æ A-12, but the singer said the child will now be known as X Æ A-Xii.
Asked by an Instagram user if she changed the name because of the law that prevents the use of numbers in names and what the new name is, she replied: "Æ A-Xii," later adding: "Roman numerals. Looks better tbh."
The couple have explained that the X stands for an unknown variable, Æ is like AI, and A-12 is a precursor to the SR-17, which she describes as "our favourite aircraft. No weapons, no defences, just speed. Great in battle, but non-violent".
Musk and Grimes have been dating for more than two years and made their red carpet debut as a couple at the 2018 Met Gala.
South African-born Musk, one of the world's most powerful and richest men, has five children with his first wife, the Canadian author Justine Wilson.
He and Grimes welcomed their first child earlier this month, with Musk confirming the news on Twitter and sharing photos of the newborn.