BTS made an appearance at "The Late Late Show with James Corden" on Tuesday to talk about their historic Grammy performance, their new album among other things. But little did the ARMY know that they will be treated with something as huge as a surprise performance of a pre-release single by the band.

Before the performance, James Corden took it upon himself to keep the ARMY on the march and treated the loyal fanbase with cupcakes while they were patiently waiting in line to see the K-pop group perform on stage. Corden figured the fans might be hungry due to the long wait in the queue, so he took a stroll outside his Los Angeles studio and started handing out cupcakes to the fans, and even hugged some of them, reports ET Canada.

A fan later shared on Twitter that one of the boxes had "Big Love to the BTS Army" written on it. The fans, who were already surprised with Corden's gesture, were left perplexed when the K-pop boy band started performing their new single "Black Swan" during the show. The stunning barefoot performance marked their first performance of the song.

BTS's choreography in the song video features the members as each other's mirrors and shadows, similar to the theme of their album "Map of the Soul," and ends with the members in human formation representing a black swan.

K-pop group BTS
The global prominence South Korea's BTS has reached unprecedented heights this year Photo: AFP / Ed JONES Ed Jones/AFP

And while RM, V, Jimin, Jungkook, J-hope, Jin and Suga, all looking dapper in black suits, did not miss a beat during their performance, they revealed what they do when they occasionally forget their dance moves. While Jin joked they immediately ask for forgiveness, J-Hope said he "doesn't care."

The seven-member band also spoke to Corden about their upcoming album "Map of the Soul: 7." RM shared, "The title 7, it's been 7 years since our debut, there's 7 members...it's a really special number for us," adding that they have practiced very hard for the album. V added: "We want our ARMYs to be happy through our music."