A demo for the main melody was first heard in an impromptu demo live stream hosted by the band, and was eventually released as part of Demos Vol. 1: Music To Kill Bad People To. The demo version consists of a jam on the main theme and was later split into three songs. On April 3rd, 2017, a Facebook user named “Blinky Bill” posted a link to a playlist of demos on Soundcloud called “Polygondwanaland” in the Facebook King Gizzard fan group. Alongside demos for “Crumbling Castle” and the “Polygondwanaland” suite were two tracks called “Spanish,” each one given a different number. “Spanish III (3)” was the fifth song in the playlist. While the Polygondwanaland demos were ripped by fans, the others were not, making it unclear what they were exactly. That said, “Spanish III (3)” can be inferred to be “Sketches of Brunswick East III” due to the connection with the album title inspiration, Sketches of Spain by Miles Davis. “Blinky Bill’’ was later revealed to be Stu, who requested that the demos not be leaked as they were accidentally shared to the public group.
The studio version was performed by Alex Brettin (electric guitar), Cavs (drum kit 1/drum kit 2/bongos/maracas/floor toms), Cook (fretless bass) and Stu (electric guitar/bass/Mellotron/flute) and was released on August 18th, 2017.

According to current setlist data, King Gizzard has never played the song live. Mild High Club may have played the song during their own shows.