The strapless silk taffeta dress, by designers Elizabeth and David Emanuel - who also designed Diana's frothy wedding gown - is expected to fetch between 30,000 pounds and 50,000 pounds ($36,000 to $61,000) at Tuesday's auction.
It's part of a collection that includes the blouse Diana wore for her official engagement portrait in 1981, and the cotton toile prototype of her wedding gown, used to ensure the fit was just right.
The black gown was worn by Diana at age 19, on her first official outing after her engagement to Prince Charles was announced. Its revealing cut and striking color caused a minor scandal - but also made Diana a media darling.
