One of the nineties most recognizable K-pop groups R.ef�and ZE:A�collaborated on 'Immortal Song 2'.

It's been 15 years since R.ef's Sung Dae Hyun�last performed, and his collaboration with hoobaes�ZE:A was his return to the stage. They sang R.ef's hits "Heartbreak" and "Official Breakup".�

Nervous before the performance, Sung Dae Hyun stated, "I'm not sure why I'm here." Despite his worry, he and ZE:A won their round against Kim Yong Jin�and 015B, but in the end, Hyun Jin Young, Moon Hee Jun, and Eun Ji Won�took the final win.

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Check out their performance above!