This post contains spoilers for "Harry Potter and the Cursed Child."

In "Harry Potter and the Cursed Child," the new play co-written by J.K. Rowling set 19 years after the last "Harry Potter" novel, we have a new villain. Delphi is the daughter of Lord Voldemort and Bellatrix Lestrange, and she wants to change the past so that her father can rule the world.

But where was Delphi for the past couple of decades? Apparently, she spent her early years under the care of Euphemia Rowle.

We know about the Rowle name because of Thorfinn Rowle, one of the Death Eaters who pledged allegiance to Voldemort. We also know the Rowle name is one of the so-called "Sacred Twenty-Eight" pure-blood families, meaning they supposedly aren't descended from any Muggles.

But Euphemia Rowle doesn't show up in ANY of the "Harry Potter" novels. But she does show up in one place: a fanfiction written by someone who seems to be named Alison S. Green, posting under the name notwilde on InsaneJournal.

As far as I can tell, the name doesn't show up anywhere else on the internet, even though "Cursed Child" has been in previews on stage in London for weeks.

There's a lot of "Harry Potter" fan fiction out there. It's cool, but not that crazy that someone came up with the same character name as J.K. Rowling. But what makes it eerie is that the details of Rowling's Euphemia Rowle and the details of the fan fiction's Euphemia Rowle totally match up.

The fan fiction comes in the form of a character sketch of a (also made-up) Death Eater named Oscar Robert Ketteridge. He graduated from Hogwarts (Slytherin) in 1965, and married Euphemia Rowle a few years later. He fell in with Voldemort while pursuing her:

He always leaned more toward the society side of his ancestry, however, fascinated by blood purity, magical history, and, as his reputation grew, Lord Voldemort. It was his relationship with Euphemia that lead him to the Dark Lord, however inadvertently. When he was courting her, he was intent on making a good impression on her father, Acastus, and some of his honest beliefs concerning Muggles, Muggleborns, and blood shone through.

Euphemia graduated in 1967, which puts her in her 30s when Voldemort was at the height of his power. It also means she was rather old when raising Delphi, which makes sense. Delphi made Euphemia sound like a neglectful guardian who had better things to do than take care of a child: "She didn’t like me much," Delphi said. "Euphemia Rowle . . . she only took me in for the gold."

It's hard to tell when exactly the fan fiction was posted. The post date was manually changed to the year 2020. But the book version of "Harry Potter and the Cursed Child" came out just hours ago, as of writing, and it's unlikely that the author wrote such an extensive fan fiction in that amount of time.

It's possible that Green saw the play's previews and then wrote her fan fiction. However, at the bottom of the post, she notes that her writing used little information from the "Harry Potter" canon and is instead "OC," or "original content."

UPDATE: Green said she created the character as part of a "Harry Potter"-themed roleplay game called "Days That Were," where users role-played as characters who interacted with each other through journal entries. She came up with the name "Euphemia Rowle" based on the Rowle family, which she knew was already a pureblood name.

"Ultimately the name is a coincidence," Green wrote in an email. "[Barring], of course, that J.K. Rowling was a secret fan of "Days That Were" [and] was paying homage, hahaha!."

Another member of the roleplaying group told INSIDER it began in 2011, predating "Cursed Child" by half a decade.