“Bohemian Rhapsody” has a structure that really resembles nothing else. No classic chorus, no recognisable verse-chorus pattern, but three distinct worlds presented one after another: a gentle ballad, an operatic section filled with layered voices, and then a full-on rock explosion. For a single from 1975, that was genuinely strange.

The operatic section required an enormous number of recording sessions, because the band members had to re-record their vocal parts again and again to build up all those vocal layers. Technically, that was a considerable undertaking for a pop song at the time.

Then there is the length. Nearly six minutes, at a time when record labels preferred shorter tracks that fitted neatly into radio schedules. And yet it worked.

The accompanying music video, made at a time when promotional videos were far from standard, helped the song reach a much wider audience. What began as an artistic gamble against all conventions grew into one of the most-played songs in rock history. Not bad for a song that was arguably too long, too strange and too difficult to categorise ever to become a hit.