Sunmi and Red Velvet's Seulgi reunited backstage at 'Music Bank'.

Fans know the two idol stars were castmates on JTBC's 'Secret Sister', and they recently got to reunite as Sunmi made a comeback with "Lalalay" and Red Velvet returned with "Umpah Umpah". On August 30, Sunmi shared the photo below along with the message, "With my dongseng Kkang Sseulgi." 

In the photo, Sunmi holds an autographed copy of Red Velvet's new album 'The ReVe Festival: Day 2', and the message says, "Hello, this is Red Velvet. We're excited our promotions overlap yours! The song 'Lalalay' is amazing. The performance and visuals feel brand new. Very cool! Let's stay healthy, and enjoy our promotions together."

Stay tuned for updates on Sunmi and Seulgi!