Sotheby's says it is auctioning about 3 million pounds ($4.6 million) worth of jewelry once owned by Wallis Simpson, the American socialite who became Duchess of Windsor.

The 20 pieces belonged to Simpson and King Edward VIII, who abdicated to marry Simpson in 1937. The pair then became known as the Duke and Duchess of Windsor.

The pieces on sale include a Cartier heart-shaped emerald, ruby and diamond brooch, with the initials W.E. (Wallis, Edward) commissioned in 1957 to mark their 20th wedding anniversary.

A Cartier onyx and diamond panther bracelet and a flamingo clip encrusted with multicolored jewels will also go under the hammer.

Sotheby's declined to discuss the identity of the sellers. It said Thursday the sale would take place Nov. 30 in London.