The main proponents of this theory have been: Dom Calmet (1672 † 1757),[3] Nicolas Viton de Saint-Allais (1773 † 1842)[4] and more recently Michel Dugast Rouillé (1919 † 1987)[2] and Henry Bogdan.

[5] The main proponents of the Gerardide-Matfriding theory are: Eduard Hlawitschka,[6] George Poull[7] and partially the Europäische Stammtafeln (which however does not take into account the kinship with the Girardides).

[8] The Renaissance dukes of Lorraine tended to arrogate to themselves claims to Carolingian ancestry, as illustrated by Alexandre Dumas, père in the novel La Dame de Monsoreau (1846);[9] in fact, so little documentation survives on the early generations that the reconstruction of a family tree for progenitors of the House of Alsace involves a good deal of guesswork.

Louis XIV's imperialist ambitions (which involved the occupation of Lorraine in 1669–97) forced the dukes into a permanent alliance with his archenemies, the Holy Roman Emperors from the House of Habsburg.

Apart from the core Habsburg dominions, including the triple crowns of Austria, Hungary and Bohemia, several junior branches of the House of Habsburg-Lorraine reigned in the Italian duchies of Tuscany (until 1737-1796, 1814-1860), Parma (1814-1847) and Modena (1814-1859).

In 1900, Archduke Franz Ferdinand of Austria (then heir presumptive to the Austro-Hungarian throne) contracted a morganatic marriage with Countess Sophie Chotek.

[citation needed] Charles II died without male heir, the duchy passing to Isabella, Duchess of Lorraine, consort of Naples by marriage to Duke René of Anjou.