An antique diamond riviere named `Lady Mount Stephen` and owned by Princess Margaret, Countess of Snowden will be part of an auction held by Christie`s in London, June 13 and 14. The necklace is estimated at $349,000-$523,000. Also available will be a five-row art deco pearl and diamond necklace and a marquise cut 5.17-carat diamond ring. The ring is expected to bring upwards of $105,000. Another special item up for auction is the "Poltimore Tiara` dating to the 1870`s and created for Florence, Lady Poltimore, the wife of the second Baron Poltimore. The princess wore this tiara on her wedding day, truly making the memorabilia factor significant in the auction. The estimate for this piece is $262,000-$349,000. Francois Curiel, deputy chairman of Christie`s and international head of jewelry says the "Christie`s is honored to have been instructed to sell jewelry and works of art from the private collection of H.R.H. The Princess Margaret, Countess of Snowdon. We will stage an auction that pays tribute to her glamorous style and beauty."Should be lovely!