Guns N’ Roses surprised fans with a rare performance of the Chinese Democracy-era cut “Silkworms” during their performance at Fenway Park on Tuesday night.

Though Axl Rose introduced “Silkworms” as “a new Guns N’ Roses song,” its origins actually date back two decades. The song was first performed live way back in 2001, and various versions have since leaked online. Tuesday night’s setlist referred to the song as “Absurd,” but its chorus clearly pulls from “Silkworms.”

Guns N’ Roses are known to be working on a new album, their first featuring Axl Rose alongside Slash and Duff McKagan since 1991’s Use Your Illusion I and Use Your Illusion II. Whether or not “Silkworms”/”Absurd” finds its way on to the album’s final tracklist remains to be seen.

In the meantime, Guns N’ Roses will spend the next couple of months touring America alongside Wolfgang Van Halen’s solo project Mammoth WVH. Tickets to their upcoming shows can be purchased here.