The order was founded with royal grand-ducal decree on 31 March 1858 by King-Grand Duke William III. The sovereignty of the order was to be shared between both branches of the House of Nassau, by virtue of an agreement between William III, King of the Netherlands and Grand Duke of Luxembourg, and Adolphe, Duke of Nassau and future Grand Duke of Luxembourg.[1] The order originally included only one grade (i.e. Knight), but was increased to four by William III in 1873: