The Princes von Altenburg are the male line descendants of the late Archduke Clemens Salvator of Austria-Tuscany, one of the children of Archduke Franz Salvator and Archduchess Marie Valerie (Franz Josef and Elisabeth's daughter).
He in 1930 married morganatically to Countess Elisabeth Rességuier de Miremont, and the following year he took the title of Prince von Altenburg, which later in 1949 was confirmed on him and his descendants by Archduke Otto, the Head of the Imperial Family.
On the same occasion in 1949 he also confirmed the title of Princes von Altenburg to the wife and the children of Archduke Karl Albrecht of Austria-Teschen.