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It comes to sale at Sworders of Stansted Mountfitchet on December 3 together with a series of letters to Mary Marshall from the Duke and Duchess of Portland documenting her time at one of Nottinghamshire's grandest country houses.

The Archduke and his wife Sophie were regular visitors to Welbeck and the brooch (marked for Vienna 1874-1922 and in a fitted case by A E Köchert, Wien) was probably given following the house party they attended on November 22, 1913 alongside the Duke and Duchess of Devonshire, Lord and Lady Salisbury and Arthur Balfour, the Conservative Prime Minister.

Only six months later, on June 28, 1914, both Ferdinand and Sophie were assassinated in Sarajevo, the shots notoriously credited with triggering the First World War.

The estimate is £800-1200.