On the November 13 broadcast of JTBC's 'Knowing Brothers', 2AM surprised the cast members, the guests, and even viewers by appearing as special performers!

On this day, the 'Knowing Brothers' members invited some of their closest friends to hold a school festival. But halfway through the festival, MC Shindong welcomed some very special musical guests!

All four members of 2AM emerged in neat, black suits as they took the stage, singing "Should've Known" and "No Good in Good-Bye" live. The cast members and guests were blown away by the high-quality live vocals of 2AM. 

Afterward, the 2AM members also participated in the signature 'Mixed-Music' quiz round, lending their voices for the segment. 

Check out 2AM's surprise appearance on this week's 'Knowing Brothers', above and below! Meanwhile, 2AM most recently returned with their brand new mini album 'Ballad 21 F/W' and double title tracks, "Should've Known" and "No Good in Good-Bye".