Grimes has confirmed her newborn son's very unusual name.
The singer, real name Claire Boucher, and her boyfriend Elon Musk welcomed their first child together on Monday, with the tech mogul proudly sharing snaps of the new arrival on his social media pages.
Elon had previously told a fan asking after the baby's name that they'd called him X Æ A-12 Musk, but it was presumed he was joking.
However, Grimes took to Twitter on Tuesday night to confirm the bizarre moniker and explained the meaning behind it.
"X, the unknown variable," the 32-year-old wrote. "Æ, my elven spelling of Ai (love &/or Artificial intelligence).
"A-12 = precursor to SR-17 (our favourite aircraft). No weapons, no defenses, just speed. Great in battle, but non-violent. (A=Archangel, my favourite song) (metal rat)."
She did not indicate how to pronounce the name.
While the baby is Grimes's first child, Elon is no stranger to fatherhood. The 48-year-old shares five sons with his ex-wife, Canadian author Justine Wilson.