The 66-year-old, who is currently touring India and Sri Lanka with Prince Charles, was at the dinner for Commonwealth Heads of Government in the capital Colombo hosted by her husband.
She wore the Boucheron tiara to "mark the historic moment that Prince Charles first hosted the summit in her honour", according to sources.
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Camilla matched the glittering headpiece with diamond earrings and a bracelet. She wore an aqua Bruce Oldfield chiffon beaded evening gown for the evening.
The Greville tiara features a honeycomb-pattern design and was made by Boucheron jewellers for British society maven Margaret Greville.
She left it to the Queen Mother when she died in 1942.
In 1953 the Queen Mother had the height of the tiara increased by adding a number of brilliant cut diamonds and a single marquise cut diamond.
The event saw leaders of Commonwealth nations meet as part of a three-day summit hosted by the Prince of Wales.
This was not the first time that Camilla has worn the beautiful piece.
The busy Duchess wore it when she attended the State Opening of Parliament for the first time in May 2013.
She also wore it to the inauguration of King Willem-Alexander of the Netherlands in April 2013.