The song was announced with the tracklist of O'Neill's first album released under the stage name "Nightmare Boy" on August 1, 2014. Plans for the album were later scrapped in favor of a four track EP in which the track did not make the cut for.
A snippet was released by O'Neill on December 17, 2014 through Instagram. The full song leaked on September 22, 2015.
On October 1, 2021, O'Neill played the song during an Instagram Live. His fiancé, who was recording the live, hinted that the song could possibly still see release someday.
On October 6, it was revealed that the song would be officially released on Barrie-James' upcoming album.
In an interview with the Scottish Sun, O'Neill explained that the song was written in 2012, and had asked Del Rey to provide vocals for the second verse. He also revealed that he reinitiated the contact between him and Del Rey in 2020/2021, as he requested permission to use "Riverside" on his upcoming album. In return, she asked if she could use "those four songs we did together" for her own album. These being "Living Legend", "Nectar of the Gods", "If You Lie Down with Me", and "Cherry Blossom". Of "Riverside", O'Neill also said, “There is no way I could have just put it out with just me singing it on my own as I didn’t want to get attacked by the Lana Del Rey fanbase."
- Album version — 3:27
- Early version — 3:46