This cased Austro-Hungarian gold and enamel brooch/pendant with a diamond-set monogram and coronet was the gift of Archduke Franz Ferdinand to Mary Marshall, the head housekeeper at Welbeck Abbey, country residence of the Dukes of Portland, from the 1890s until her retirement in 1923.

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.