If there was any doubt left, billionaire Elon Musk and musician Grimes legally, actually, 100 percent named their child X AE A-XII. "X" being the kid's first name, and "AE A-XII" their middle, and "Musk" their last.

That's according to a birth certificate TMZ obtained.

X AE A-XII is actually a slight shift from what Musk first announced — he initially said the name was X Æ A-12 — because California doesn't allow special symbols or numbers in a legal name. Still, the overall sentiment of the name is the same.

Musk has explained, how, exactly, he and Grimes went with such a... unique... name for the child born last month.

"First of all, my partner is the one who, mostly, actually came up with the name," Musk told Joe Rogan on the comedian's podcast last month. 

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"I mean it's just X, the letter X," Musk said. "And then the AE is like pronounced 'ash'... yeah... and then A-12 is my contribution."

Tweet may have been deleted

In case you were wondering, A-12 stands for the Archangel 12, the precursor to the SR-71 aircraft, which Musk called "the coolest plane ever" on Rogan's podcast.

SEE ALSO:Elon Musk announces the birth of his baby in the most Elon Musk way possible

So, yeah, the child's name is official and it's definitely a bit of a mouthful.

But don't worry, they're already using a nickname.

Grimes told Bloomberg in May that she calls her baby “Little X” for short.