"Lonely" is a song by South Korean singer-songwriter Jonghyun featuring Taeyeon, a member of girl group Girls' Generation. It was released on April 24, 2017 through SM Entertainment, and served as the lead single for his second compilation album, Story Op.2. It was written, composed and arranged by Jonghyun in collaboration with Wefreaky, Monotree and Imlay. "Lonely" was the last single released by Jonghyun during his lifetime and experienced a surge in popularity following his death by suicide on December 18, 2017, reaching number one on Gaon Digital Chart. It has come to be viewed as emblematic of his struggles with mental health. Background and release On April 19, 2017, SM Entertainment announced that Jonghyun would be releasing his new song "Lonely" on April 24, and that it was to be a duet with Taeyeon, with whom Jonghyun had previously collaborated for the 2014 SM the Ballad song "Breath". It would serve as the title track to Jonghyun's new compilation album, Story Op.2, a follow-up to 2015's Story Op.1. Unlike his other releases, which present an "idealized" version of himself, the songs on the Story Op albums are intended to showcase a side of Jonghyun that is "more ordinary and human". A teaser was released on April 21 on the SM Town YouTube channel, followed by the subsequent release of the song and its music video three days later. The music video, which was filmed in Los Angeles, depicts Jonghyun alone on the beach and in a large house, conveying feelings of emptiness. "Lonely" was not promoted on music shows; however, Jonghyun and Taeyeon performed the song live on You Hee-yeol's Sketchbook on May 13 in what would be their only joint performance. Jonghyun later performed the song by himself at his solo concert The Agit. Composition "Lonely" was written, composed and arranged by Jonghyun. Wefreaky, Monotree and Imlay also made contributions to the composition and arrangement. It has been described as "a heartbreaking, piano-guided midtempo ballad that reflects on the feelings of things never getting better amid a sense of immense loneliness." Jonghyun wrote "Lonely" expressly because he wanted to sing with Taeyeon, and tailored the song's composition to her. He said, "I wanted to take the aura that she has, where she’s a bright and happy person with a sensitive and lonely side as well, and put that in the lyrics. I thought of her while I was