Celebrity couples appear to enjoy giving their children unusual names. Gwyneth Paltrow and Chris Martin called their daughter Apple because the Goop founder thought it “sounded sweet,” while Liam Payne named his son Bear because he liked the concept of his son having a distinctive name.

Ed Sheeran revealed the significance of his daughter’s name, Lyra Antarctica. The musician added that his wife, Cherry, has a unique name, which he admires. Sheeran then explained that his daughter’s middle name was inspired by the fact that he had just returned from a trip to the continent before learning his wife was expecting.

Elon Musk, the founder of Twitter, and musician Grimes named their first child X Æ A-XII, or “X,” for short. Grimes explained the meaning of the name in a tweet.

“X, the unknown variable; Æ (love &/or Artificial intelligence); A-12 = forerunner to SR-17 (our favorite aircraft),” she wrote. When it was later reported that Grimes and Musk had another child, a daughter, people wondered if her name would be as distinctive as her older brother’s.

Grimes disclosed the new name of their daughter, Y.

On March 23, Grimes revealed that she and Elon Musk have decided to change the name of their second daughter. “She’s Y now, or ‘Why?’ or just ‘?” tweeted the “Player of Games” singer. According to the singer, the new name corresponds to “curiosity” and “the perpetual question.”

She was reacting to a fan’s tweet calling her kid “Sailor Mars.” It has already been revealed that Grimes and Musk are fans of the manga series “Sailor Moon,” as they frequently refer to their daughter as “Sailor Mars,” which explains the fan’s post that the singer responded to.

The name change doesn’t seem that surprising given that Vanity Fair previously claimed that “Y” was a nickname for the Twitter CEO and the singer’s second daughter — who was initially named Exa Dark Siderael — before they publicly disclosed her full name. The new name also corresponds to Grimes and Musk’s first child, X, making the children “X” and “Y.”