A selection of Princess Diana's dresses will sell at Kerry Taylor Auctions on December 12.
Among the highlights is a purple velvet Bruce Oldfield gown she wore on a state visit to Portugal in 1987.
It was last sold at the charity auction of her dresses in June 1997, where it realised $26,450.
It's now expected to sell for around £50,000-70,000 ($63,162-88,427).
The auction house comments: "At the official dinner given by Portugese president Mario Soares at the Ajuda Palace, Lisbon, she accessorised the gown with a stunning diamond tiara which had been given to her by her mother in law, H.M. the Queen and dazzled all present.
"The dress since purchase has been occasionally exhibited for charity and carefully stored away in tissue paper.
"The last person to wear the gown was the Princess as, out of respect, the purchaser never wore it."
A tartan wool dress by Caroline Charles is valued at £6,000-9,000 ($7,579-11,369).
Diana wore this ensemble to the 1982 Braemar Highland Games - the year after her marriage to Prince Charles.
The consignor acquired it from a dress shop at some point during the 1980s. The designer has affirmed the lot is one of kind.