The Delhi Durbar Tiara, made in 1911 for Queen Mary to wear at the Delhi Durbar in the same year, will be shown to the public for the first time as part of a special exhibition of Queen Elizabeth's diamonds at the Buckingham Palace from Saturday.
The exhibition - Diamonds: A Jubilee Celebration - will showcase more than 10,000 diamonds, including a number of the Queen's personal jewels and pieces from the Royal Collection.
The Delhi Durbar was held in 1877, 1903 and 1911.
The 1911 Delhi Durbar was held in December to commemorate the coronation in Britain of King George V and Queen Mary, and their proclamation as Emperor and Empress of India. It was attended by almost every ruling prince, nobleman, landed gentry and other persons of note in India.
The Delhi Durbar Tiara was part of the Queen's parure of emeralds and diamonds made for the occasion by Garrard & Co Ltd. The parure included a necklace, stomacher, brooch and earrings. King George V referred to the Delhi Durbar Tiara as 'Mary's best tiara'.
Queen Mary loaned the tiara to Queen Elizabeth I in 1946 for the South African Tour in 1947, and it remained with her until her death in 2002. In 2005, it was loaned by The Queen to The Duchess of Cornwall.
Exhibition curator Caroline de Guitaut said, "The exhibition shows how over the past three centuries monarchs have used diamonds to display magnificence, whether in personal adornment or as a statement of power."