On August 25, the drummer took to his personal Instagram account to share images of him and Seulgi exchanging signed copies of their latest albums backstage while shooting the music show.
"Long time no see!" he wrote in a caption directed to Seulgi. "It feels like it was just yesterday that we were in high school playing games via iPad, and it's great to be able to see you like this. Fighting!"
The two idols, both born in 1994, were good friends while in the same grade at Seoul's esteemed School of Performing Arts (SOPA). Other notable K-pop alumni from their graduating class include KARA's Youngji, Sulli, Suzy, and Girl's Day's Hyeri.
Meanwhile, The Rose and Red Velvet are currently promoting their latest singles "Red" and "Umpah Umpah," respectively.
Check out Hajoon's Instagram post below!