What is the name of a Korean love song (male/female duet) popular in 2006?

I'm searching for a Korean male/female duet that was popular at the end of 2006. It was a ballad that had a haunting/soulful melody. I was living in Mongolia at the time and was not able to catch the artist or song name. Vague, I know, but if anyone has any ideas I'd be happy to listen to them. ^^