Fans are already confused about the name of Elon Musk and Grimes' baby son - and now it turns out the unusual name won't be legal in California.
The 32-year-old singer Grimes tweeted that their son's name, X Æ A-12, was partly inspired by the couple's favourite aircraft, according to the Daily Mail.
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"A-12 = precursor to SR-17 (our favourite aircraft)," she wrote, but Musk was quick to correct her, pointing out that the spy plane is actually called an SR-71.
"I'm recovering from surgery and barely alive so may my typos b forgiven but, damnit. That was meant to be profound," Grimes, who gave birth on Monday, replied to her partner.