London, England (CNN) -- They are the jewels of a royal love affair, one that led Britain's King Edward VIII to abdicate the throne more than 70 years ago so he could marry the woman he loved.
Now, the diamonds, gold, and precious gemstones that expressed the love between Edward and American Wallis Simpson are going up for auction.
The 20 items being offered at Sotheby's in London on Tuesday include 11 pieces by Cartier, some of which are estimated at more than £1 million ($1.5 million) each.
"The offering comprises not only incomparable examples of the genius of Cartier in collaboration with the Windsors, but also pieces whose inscriptions tell the story of perhaps the greatest love story of the 20th century, the romance that led Edward VIII to abdicate the throne of Great Britain," said David Bennett, the chairman of Sotheby's Jewelry in Europe and the Middle East.
The couple commissioned jewels from the great European jewelry houses during their courtship in the 1930s and after they were married, Sotheby's said.
Cartier was one of their favored jewelers, and the company's high jewelry director Jeanne Toussaint created some of her best work just for the couple, who came to be known as the Duke and Duchess of Windsor.
One of the pieces she created was an onyx and diamond bracelet in the form of an elongated panther. Designed in 1952, the bracelet was among the finest of Toussaint's "great cats" jewels and is in the sale at an estimated £1-1.5 million ($1.5-2.3 million).
Also up for sale is a diamond flamingo brooch with feathers of rubies, sapphires and emeralds, and a beak of citrine. The brooch, also estimated between £1 and 1.5 million, was the showpiece of an earlier sale of the couple's jewels, held in Geneva in 1987.
All the items up for auction Tuesday belonged to a single owner, but Sotheby's did not disclose that person's identity.
Edward had been on the throne for just 11 months when he decided to give up the crown in December 1936 to marry Simpson, an American divorcee. He chose to abdicate because, as supreme governor of the Church of England, he was not permitted to marry a divorced woman.
The abdication speech he gave Dec. 11, 1936, revealed his love for the woman who would later become his wife.
"I have found it impossible to carry the heavy burden of responsibility and to discharge my duties as king, as I would wish to do, without the help and support of the woman I love," Edward said.
The auction includes a favorite bracelet of Simpson's, made of diamonds and supporting nine gem-set Latin crosses -- each with an intimate inscription on the back, Sotheby's said.
The crosses represent special moments in her life, including her marriage and the assassination attempt against the king.
A heart-shaped brooch of rubies and diamonds was commissioned for the couple's 20th wedding anniversary and features the initials W.E. -- for Wallis and Edward -- in emeralds on the front.
Cartier also created a six-piece diamond-encrusted dress suite comprising a pair of cufflinks, three dress buttons and a stud, given by Simpson to Edward in 1935 to wear for the Royal Silver Jubilee celebrations and his birthday.
Each cufflink features an E on one end and a W on the other. One of the buttons is inscribed on the back with the phrase "Hold Tight," a favorite phrase of the couple in their correspondence before marriage.
Another gift Simpson gave to her husband traces the routes of European trips they had taken together on an 18-carat gold and gem-set cigarette case. Each city is marked with a gem or diamond and is connected to the next by enamel lines.
The inscription on the back reveals it was a Christmas present in 1935.
Other items in the sale include a purse made by Van Cleef and Arpels of gold mesh, rubies, turquoise and diamonds, and a series of silver items and medals once owned by Edward.