Every night, Jaehyun and Johnny, two members of the K-pop boy band NCT, host a radio show called NCT Night Night on Korean radio station SBS Power FM.
The two concluded their show on Monday with the song "Caroline" by American rapper Aminé.
The show's video livestream continued for some time after the two signed off, and Jaehyun can be seen singing along and mouthing a line which includes the n-word. It is unclear whether he actually said the word aloud, as both the DJs' microphones had been turned off.
Fans watching the livestream couldn't believe what they had witnessed.
And voiced their disappointment in him.
They felt that Jaehyun had no excuse as he lived in the US for four years.
And called out other fans who tried to shift the blame onto Johnny and in other cases, Aminé.
People are now demanding an apology.
BuzzFeed News has reached out to Jaehyun's representatives for comment.
Kassy Cho is a reporter for BuzzFeed News and is based in London.