South Korean megastars BTS reunited Saturday for their first show in nearly four years in front of enormous crowds in Seoul for a K-pop extravaganza livestreamed to millions more worldwide. Five million fans pre-saved it on Spotify,

BTS star Jin admitted he had "so many worries" about their first concert in four years, which will be available on Netflix.

All seven members of the band — RM, Jin, Suga, J-Hope, Jimin, V and Jung Kook — recently completed South Korea’s mandatory military service, and hope to reclaim their status as one of the world's bigg...