The title of Archduke ( feminine : Archduchess ) ( German : Erzherzog , feminine form : Erzherzogin ) is a rank above Duke and under King . The title of Archduke ( feminine : Archduchess ) ( German : Erzherzog , feminine form : Erzherzogin ) denotes a noble rank above Duke and below King , used only by princes of the Houses of Habsburg and Habsburg-Lorraine .