I.O.I's 9-year reunion concert sends 'Suddenly' to #1; Jeong Chae-yeon's backstage tears to air June 13

Nine years after their original run, I.O.I held a complete-group concert to mark the group's 10th debut anniversary. Title track Suddenly (갑자기) reached #1 on music charts on the day of the show.

The group formed through the 2016 audition program Produce 101. They had just an 8-month activity window. In that time they picked up music broadcast wins and rookie awards before disbanding. The 10th anniversary concert brought all nine members back together: Im Na-young, Kim Chungha, Kim Sejeong, Jeong Chae-yeon, Kim Sohye, Yoo Yeon-jung, Choi Yoo-jung, Kim Doyeon, and Jeon Somi. The setlist ran from Pick Me through Shower (소나기). Nine member teams and nine separate company staff groups collaborated on the project.

Jeong Chae-yeon was already in tears backstage before the concert began. "I thought this miraculous reunion might really be the last," she said, explaining why she broke down.

Behind-the-scenes footage from the concert airs on MBC's Jeonsimsi (전지적 참견 시점) episode 402 on Saturday, June 13 at 11:10 PM KST.