'Knowing Brothers' has released the preview for next week's episode.

The JTBC variety program has invited four epic girl group idols from all generations. The four guests are: Baby V.O.X's Lee Hee Jin, T-ara's Hyomin, Oh My Girl's Seunghee, and Gugudan's Kim Se Jung. The catchphrase of the episode is "once a girl group, forever a girl group," bringing out the timeless bond among the group members and their own individual identities as female idols. 

In the preview, the current generation girl groups sing and dance to some of the 1st generation songs. The permanent cast members of 'Knowing Brothers' also get up on their feet and join these idols. 

Stay tuned until the episode air on March 30 at 9 PM KST!