Oh No, I’m not talking about the Australian river Darling. I’m talking about Vishal Bhardwaj’s already famous song Darling from the movie Saat Khoon Maaf.
The song is actually very much based on Russian song Kalinka, a song written in 1860.
I have no idea how much Vishal is going to acknowledge this in the movie/soundtrack (I hope he does acknowledge), but that sounds very much true. You can listen to the song at the Wikipedia page, and also find a few more links to the song there.