One of the biggest hits of the 70s - and one of the saddest of all time. This week Chelsea explores a genuine classic - Gilbert O'Sullivan's 'Along Again (Naturally)'. Find out how Gilbert's storytelling and empathy as a lyricist, combined with a gorgeous harmony propelled this song to worldwide fame, with a little help from an anime series. Plus, just one word that, added to the title, perfectly captured the song's black humor.

Why This Song? is a curious new video series about pop music, and pop culture. We all obsess over music. You can find out everything about your favourite song: how and where it was made, who the artists were…But a fascinating mystery remains: the WHY of the song. Why does it even exist in this world? Why do we love it so much? Why, after all these years, do we still love it?