The young boy, who goes by the nickname X, has a Scrabble-esque name.

Elon Musk has made so many headlines that it’s easy to forget the buzzy headlines that were written when he and singer Grimes gave their son, born in 2020, a truly unique name. The boy now goes by X, the same letter as the name Musk gave to Twitter and uses in SpaceX. But his full name is more complicated: X Æ A-12.

The boy is 5 now, but back when he was an infant, his dad appeared on The Joe Rogan Experience podcast and confirmed the name’s pronunciation.

“How do you say the name?” Rogan asked. “Is it a placeholder?”

Apparently not. Musk said at the time that the name is pronounced “X Ash A Twelve.” (“Æ” is a character used in some languages, including Danish and Norwegian. It’s often pronounced “ash,” but some people pronounce each letter, saying “A E.”)

“First of all, my partner’s the one that mostly came up with the name,” Musk said of Grimes. “I mean it’s just X, the letter X, and the ‘Æ’ is pronounced, ‘Ash,’ and then, A-12 is my contribution.” He went on to say that A-12 stood for “Archangel 12, the precursor to the SR-71, coolest plane ever.”

Musk has 14 children total, with four different women, according to People. His other children with Grimes are a daughter, Exa Dark Sideræl, age 2, and a son, Tau Techno Mechanicus, age 3. 

In February, before President Donald Trump and Musk had their much-publicized falling-out, X showed up with his father in the Oval Office, where the president called the toddler a “high IQ individual.”

But the boy’s mom was not pleased.

“He should not be in public like this,” X’s mother, singer Grimes posted, according to The Standard. “I did not see this, thank u for alerting me. But I’m glad he was polite. Sigh.” 

Hear Elon Musk pronounce X’s full name

If you want to hear Musk pronounce X’s full name, you don’t have to fast-forward through much of the video. Rogan asks him to pronounce it just 37 seconds into the 2020 podcast.

Grimes tweeted a more detailed explanation of why the various parts of the name were chosen in 2020. She called X “the unknown variable,” and said that Æ was “my elven spelling of Ai,” which she explained as “love and/or artificial intelligence.” 

As for the A-12, she called the plane “our favorite aircraft,” going on to tout its “no weapons, no defenses, just speed. Great in battle, but non-violent.” Grimes also noted that the A in A-12 stood for “Archangel,” which she said was “my favorite song.” She didn’t specify which song — numerous songs are titled Archangel — but some music sites guessed she could mean the song by the band Burial. Grimes once cited Burial’s Archangel song as a favorite on her Tumblr.

She ended her tweet with the words “metal rat” and emoji of crossed swords and a rat. 2020 was the year of the “metal rat” according to the Chinese zodiac, although of course it can also simply mean “fan of heavy metal music.”

Grimes mistyped SR-17 instead of SR-71, but Musk corrected her in another tweet, writing, “SR-71, but yes.”

To which she replied, “I am recovering from surgery and barely alive so may my typos b forgiven but, damnit. That was meant to be profound.”

It’s possible the name does not appear on the baby’s official California birth certificate — at least not in the spelling that’s been shared by his parents. A California family-law attorney told People magazine that while the name isn’t illegal, the state doesn’t allow symbols on birth certificates. Apostrophes, such as in a last name like O’Connor, are allowed, and it would seem that the hyphen might also make it through. But symbols like “Æ” might cause the certificate to be rejected, and the parents would have to submit it again. 

At the time, Musk also noted that he was happy the baby was born on May 4, commonly known as Star Wars Day for the saying “May the fourth (Force) be with you.”