A purple Bruce Oldfield evening gown Princess Diana wore on a state visit to Portugal in 1987 has sold for £45,000 ($57,108) at Kerry Taylor Auctions.
It was last sold for $26,450 at the 1997 charity auction of Diana's dresses, held just a month before her death.
Bruce Oldfield designed the purple ball gown
That equates to growth of 115%.
Diana was the centre of attention at the reception.
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 Caroline Charles tartan outfit Diana wore to the 1982 Highland Games was another highlight, achieving a solid £5,500 ($6,986).
It was originally sold to a dress store in Hampshire by a relative of Sarah Ferguson, the Duchess of York during the 1980s. The designer has confirmed that the lot is one of a kind.