It’s a musical mystery that has been confounding the internet for years. But an ultra-catchy 80s-sounding song that seemingly no one could identify has finally been tracked down – in a 1986 adult movie.

A snippet of the song, known as Everyone Knows That – a low-quality, warped recording that nevertheless showed off the song’s huge pop appeal – was uploaded to YouTube in 2021 and shared on Reddit, where it sparked a hunt for the creator. Some 47,000 people became dedicated to the quest in a subreddit community. Theories abounded that the song was a lost demo by artists including Roxette and Savage Garden, or had been written for a forgotten advertisement. The Guardian, Rolling Stone and Radio 4’s Today programme were among those reporting on the search.

Reddit users began combing song publishing databases for Everyone Knows That and its other guessed-at title, Ulterior Motives, narrowing it down to a series of rights holders from the mid-1980s.

One user, south_pole_ball, found that one of the listed songwriters, Christopher Booth, had written work for pornographic films – and duly watched his oeuvre until he heard the song. “I went through each video and watched them, until I found Angels of Passion (1986),” they wrote. “To which I got to 1:07:31 and I found EKT [Everyone Knows That]”.

Booth seemed to corroborate the discovery, posting a picture of the original YouTube upload to Instagram and writing: “Well today, my mind has officially been blown:) WOW! #ulteriormotives #ekt”.

The full version of the song, credited to Booth and his brother Philip, can only be heard alongside the movie in question, accompanied by carnal sound effects, leading to hundreds of requests for an original version to be released. A re-edited, non-pornographic version without the sound effects – but still in low fidelity – has been created by admirers in the meantime.

The Booth brothers have gone on to form a successful partnership in low-budget horror films and documentaries, with Christopher continuing to deploy his musical skills as a composer on their projects.

The song was part of a wider community known as “lostwave”, with members dedicated to identifying forgotten pieces of popular culture.

“We live in a time when knowledge is freely available to us and we can consume music without much restriction,” one of the moderators of the Everyone Knows That subreddit, Bas, told the Guardian of the appeal of lostwave. “Music that is lost in pre-internet times is likely very interesting to younger people, because it’s such a foreign thing to them, to not be able to simply look up the song.”