Elon Musk announced the birth of his first child with girlfriend Grimes on Monday, May 4. (Musk also has five sons with Justin Musk (open in new tab). He later tweeted the newborn's name: "X → A-12 Musk."

In her first tweet since the birth of her first child, a baby, Grimes confirmed the name and explained each element and its significance to the couple. 'X, unknown variable,' she tweeted. 'Æ, elf spelling of Ai (love and / or artificial intelligence).'

"A-12" refers to a military aircraft, Grimes (real name Claire Bouchet) explained. The Lockheed A-12 is a now-retired reconnaissance aircraft (open in new tab) built for the CIA in the 1960s. 'No weapons, no protection, just speed. Great in combat, but non-violent," tweeted Grimes, who told the BBC that the aircraft was called the Archangel (opens in new tab) during its development. (A little Internet sleuthing suggests that she is referring to Burial's "Archangel". (opens in new tab))

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