https://en.wikipedia.org/wiki/The_Most_Beautiful_Moment_in_Life:_Young_Forever
https://itunes.apple.com/de/album/hwayang-yeonhwa-most-beautiful/id1109292307 Edit: secondary source
http://bts.ibighit.com/discography.php Edit: tertiary source
The song title is "Butterfly" (Prologue mix)".
https://itunes.apple.com/de/album/hwayang-yeonhwa-most-beautiful/id1109292307 Edit: secondary source
http://bts.ibighit.com/discography.php Edit: tertiary source
The song title is "Butterfly" (Prologue mix)".