Fabergé, Cigarette case, 1908 (source).

“…the design is not purely decorative; the snake biting it’s tail is a symbol of unbroken and everlasting love and thus it is not surprising to learn that the case was given to King Edward VII by his favorite mistress, Mrs George Keppel, in 1908. Perhaps recognising the significance of the gift, Queen Alexandra returned it to Mrs Keppel as a memento following the King’s death in 1910. Twenty-five years later, in 1936, Mrs Keppel gave the case to Queen Mary, thereby ensuring that it would remain in royal ownership.” - from the Royal Collection description