Kim Jae-joong and Gummy - (Cjes Entertainment)

JYJ’s Kim Jae-joong appeared as a guest singer at Gummy’s “Fall in Fall” concert in Seoul on Friday.

“I just came back from Gummy’s concert. Sadly, I had to sing only half of the song at the concert since I had caught a cold,” Kim Jae-joong wrote on his Twitter account. He also uploaded the YouTube video of his performance.

“Gummy had appeared as a guest at Kim’s solo concert last year, and this time, he returned her favor by communicating with the audience and singing his sweet songs at her concert,” C-JeS Entertainment said.

The two became known as a fantastic duo, like twin brother and sister, when they sang together at the concert last year. Gummy was even featured on Jae-joong’s new song “Heaven” on his repackaged album released in January.

The two have the same entertainment company and are on very friendly terms, according to an official from C-JeS Entertainment.

By Park Gyu-oh (q5park@heraldcorp.com)