On June 20th KST, netizens raised another plagiarism allegation after comparing Sung Si Kyung's "Happy Birthday to You" and Koji Tamaki's "Happy Birthday to You". Sung Si Kyung's "Happy Birthday to You" was written, composed, and produced by Yoo Hee Yeol and is currently registered under Yoo Hee Yeol's name with the Korea Music Copyright Association (KOMCA).
Netizens commented, "I thought Sung Si Kyung's song was a remake version of Koji Tamaki's song," "This is more than being 'influenced'," and "It's more suspicious as Sung Si Kyung previously said he respects that artist. Yoo Hee Yeol might have considered that."
Meanwhile, Yoo Hee Yeol has recently issued a formal apology after many raised allegations his "A Most Private Evening" sounds similar to "Aqua" by Ryuichi Sakamoto.