McCartney's 1987 single "Once Upon a Long Ago" carries with it a bittersweet tale of what could have been a historic collaboration. The song, which was part of McCartney's compilation album "All the Best!" and later released as a single, was initially composed with the Queen frontman in mind.

The story goes that McCartney had envisioned the track as a duet with Mercury. However, due to Mercury's ill health and busy schedule, the collaboration never materialized. McCartney went on to perform the song solo, and it reached No. 10 in the UK Singles Chart. 

Artificial intelligence has opened up new possibilities, allowing fans to experience a version of "Once Upon a Long Ago" featuring Mercury's distinctive voice. This not only showcases McCartney's songwriting prowess but also pays homage to Mercury's enduring legacy.
While it's true that nothing can replace the magic of a real-time collaboration between McCartney and Mercury, AI remixes offer a glimpse into an alternate universe where the two icons perform together.

"Once Upon a Long Ago" serves as a beautiful, if somewhat melancholic, tribute to the power of music and the enduring spirit of creativity that defines both McCartney and Mercury's contributions to the world of music.