The Wittelsbach cushion-shaped blue diamond that made £14.6m at Christie’s in London.

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The rare 35.56 carat cushion shaped blue diamond - the size of a postage stamp - was purchased by King Philip IV of Spain in 1664 and was included in the dowry of his daughter, the Infanta Margarita Teresa, when she married Leopald I of Austria.

It was then passed down through the Bavarian Royal family until offered at auction in 1931, where it failed to sell and then vanished only reappearing in 1962, when a jeweller refused a request to re-cut it.