(IDEX Online) - An amethyst and diamond pendant famously worn by the late Princess Diana, is expected to fetch up to $145,000 when it is auctioned by Sotheby's London later this month. The Fleur?? (C)e cross, circa 1920, set with square-cut amethyst and accented by circular-cut diamonds belongs to London-based Garrard, official jeweller to the royal family for 160 years until 2007.Princess Diana first borrowed the cross in 1987, and on many subsequent occasions, as part of a bold fashion statement.The piece is described as "Estimated total diamond weight approximately 4.25 - 5.25 carats. Largest amethyst measuring approximately 15.6 x 15.5 x 8.1mm," in a 1991 Garrard document, cited by Sotheby's.Naim Attallah, who died last year, was group chief executive of Asprey & Garrard (now Garrard). As a good friend of the Princess, he acquired the cross shortly after her death and it has remained with the family, unworn, ever since.Sotheby's will present the "incredibly rare piece of royal history" at its Royal and Noble sale on Friday 6 January. Estimate $97,000 to $145,000. Main pic courtesy Sotheby's