“Barcelona” is a single released by Queen vocalist Freddie Mercury and operatic soprano Montserrat Caballé. A part of their collaborative album Barcelona, it also appeared on Queen’s Greatest Hits III.. The song reflects Mercury’s love of opera with his high notes and Caballé’s operatic vocals, backed by a full orchestra.

https://en.wikipedia.org/wiki/Barcelona_(Freddie_Mercury_and_Montserrat_Caball%C3%A9_song)