The band reunited for over 150 fans in a surprise concert.

After performing "SWIM" on Wednesday night, the septet was back at New York's iconic Guggenheim Museum, this time hitting "2.0" from their new album "ARIRANG."

BTS reunited with Jimmy Fallon on Wednesday night to promote their new album 'ARIRANG' in New York City

Tens of thousands turned up to watch and more than 18 million people live-streamed the one-hour show - a slick teaser of the upcoming BTS world tour, with the group's easy camaraderie on display, almost as if they had not spent much of the last three years apart,

There’s more surprises in store for the BTS Army! Shortly after their much-anticipated comeback album, a new music video, a live show in Seoul and a documentary, the K-pop band announced the reboot of their popular variety show Run BTS!

BTS nearly ties both The Rolling Stones and the Bee Gees as "Swim" opens atop the Billboard Hot 100, earning the group a seventh career champion.

The song is the second track off ARIRANG to receive the visual treatment.

CNN’s Paula Newton has the latest on the fan craze over BTS’s world tour.