"Bob Dylan ran through the 18th century English folk song 'Pretty Saro' six consecutive times during the Self Portrait sessions in March 1970..."

"... but none of those versions made the final cut for the album and the song remained in Columbia's vault for the past 43 years. The track never even leaked onto bootlegs, but on August 27th, it's finally coming out on Another Self Portrait, a 35-track box set of songs cut for Nashville Skyline, Self Portrait and New Morning."

Details and video of the song here. 

Here's the old "Self Portrait." "Another Self Portrait" will come out at the end of the month.