As always, the panelists had to guess if contestants are talented singers or tone-deaf based on clues. 

On the June 1 episode, Oh Sang Eun appeared as one of the contestants. If a talented singer, she is a former girl group member from SM Entertainment. If a tone-deaf, she's an account and the daughter of Leeteuk's mom's friend. 

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While in the debate about her identity, Leeteuk added strength to the possibility of her being a former SM girl group member by saying that he recognizes her. 

After a long discussion, Oh Sang Eun finally revealed her identity by performing So Chan Hee's ''No Choice But To Let You Go''. 

Oh Sang Eun turned out to be a talented singer and surprised all with her amazing vocals. 

Following the performance, Oh Sang Eun explained that she debuted under SM Entertainment in the girl group Shinvi in 2002. Oh Sang Eun also shared that she started training in 8th grade and has met Leeteuk during training.

Leeteuk reminisced the old days, and asked Oh Sang Eun, "Didn't you used to like me?" She answered, "I have no idea what you're talking about."

Since her debut and departure from Shinvi, Oh Sang Eun has been promoting solo with the stage name Nemo, performing in musicals, etc. However, Oh Sang Eun explained that she thought about quitting her singing career as she struggled to find opportunities. 

Watch her appearance on 'I Can See Your Voice 4' in the clip above.