May 6 (UPI) -- Grimes is sharing the meaning behind her son's unique name.
"X, the unknown variable," she wrote. "Æ, my elven spelling of Ai (love &/or Artificial intelligence) A-12 = precursor to SR-17 (our favorite aircraft). No weapons, no defenses, just speed. Great in battle, but non-violent. A=Archangel, my favorite song."
Grimes later responded to someone who said "you realize this is a human child and not an EP right."
"I think it sounds like the name of the main character in the story," Grimes replied. "I hope he vibes with that. Ok, going back into the pain/beauty reverie for sum time, just came on to add my thoughts. Peace to all."
Fans speculated online that Grimes and Musk will call their son Ash Archangel. Æ is pronounced "Ash" and the A-12 aircraft was nicknamed "Archangel," as Musk confirmed in a tweet.
Musk said Tuesday evening that baby X Æ A-12 is "happy, healthy & cute as a button."
Musk has five other sons, twins Griffin and Xavier and triplets Damian, Saxon and Kai, with his ex-wife Justine Musk. Grimes announced her pregnancy in January, and later said she won't raise her child to be "too spoiled."
Grimes and Musk made their red carpet debut as a couple at the 2018 Met Gala.