When you tune into the classic '90s sci-fi series The X-Files, it's safe to assume mystery is afoot. Typically it's aliens or other paranormal phenomena.

But how often is the show the source of the mystery?

A song playing in the background of one episode has fascinated and eluded fans for more than two decades as they sought to track it, and the musicians, down. Now that mystery has finally been solved.

The saga began with Lauren Ancona lounging on the couch at her parents' house outside of Philadelphia. She was zoned out on her phone, with an old episode of The X-Files playing in the background, when a particular tune from the show caught her ear.

"It was too good to be background," she told NPR. "And I pause it and, like, rewind it and was like, 'Oh, what is that?'"

It was in an episode from 1998 — season 6, episode 5, titled Dreamland II — that was the second part of a storyline where special agent Fox Mulder swaps bodies with an Area 51 employee. The scene in question takes place at a bar in Nevada where a country-western love song plays in the background.

Ancona said the lyrics were what grabbed her attention.

"The lyrics were so specific that, you know, they could obviously be interpreted as if they were singing to or about an alien or some extraterrestrial life or something that isn't human," she said.

Ancona tried an app on her phone to identify it. Nothing. When she looked up the lyrics, she came across other X-Files fans who had been searching for the same song – a mystery that had gone unsolved for 25 years.

She posed the question on X (formerly known as Twitter) and it exploded. Within days, Ancona got her answer.

Composer Rob Cairns came across the viral post and reached out to his friend who just so happened to be the co-writer behind that song, Dan Marfisi.

"He said, 'You might want to check out this Twitter thread, and if you jump in, you will be a hero,'" Marfisi told NPR. "So I went and got my cape, and I logged on, and it was a party."

It turns out people were having trouble finding the song because Marfisi co-wrote the song with Glenn Jordan for the background of this specific X-Files scene. They had titled it Staring At The Stars.

"We had a directive to write something that would fit both an alien and a human being," Marfisi said. "And we kind of looked up in the sky and said, what's up there besides aliens? And we found stars ... that was our brainstorming session."

A quick session, at that. Jordan and Marfisi told NPR they wrote and produced the song in about four hours.

"So we turn it in... and that was the end of it," Marfisi said. "We put it to bed and here we are 25 years later."

For musicians like them, writing a song like that is just a day in their life – they never expect them to get this kind of attention. And they're thrilled. Jordan estimated that he has music in more than 2,000 episodes of television shows and movies.

"It was just a 'Wow,'" Jordan said. "What made it even a little spookier is I teach composition and I have a student in Spain and he [had just] gotten the entire X Files [series]. And I just said to him, 'Well, you know, I've got a song and this particular one you should check out.' And I was talking about Staring at the Stars a day before Dan called me and said, 'Hey, guess what?'"

"You always want to feel feedback from who you're making music for," Marfisi said. "And we watched it unfold on the interwebs and it was unique ... it's a joy."

Jordan still had a copy of the song on a CD in his house. Inspired by the newfound interest, Marfisi drove over to snag the copy, and the duo reunited for the first time in five years.

Now you can listen to the full song on YouTube. Jordan and Marfisi told NPR they're planning to make it available on music streaming services soon, and are mulling the idea of releasing some other country tunes they worked on together back then.

Ancona, like the other X-Files song truthers, are thrilled Staring at the Stars has been unearthed and shared with the masses.

"I mean, what is better than discovering this thing that people have been looking for 25 years for," Ancona said. "And they're able to post it online in less than four days. It was just such a remarkable progression."