The current heir of Catherine de Medici is Herzog Franz von Bayern, Duke Francis of Bavaria.
He is thus the heir of any claims she might have had to the crown of Portugal and the Algarves.
Interestingly, he is also the legitimate, direct, senior line heir of the Stuart dynasty, and therefore the crowns of England, Scotland, and Ireland, as well as the English royal house's right to the French throne (derived from Edward III and Henry V) and the Duchy of Normandy (derived from his distant ancestor William the Conqueror, Duke of Normandy).
If I'm not mistaken, the Viking-Norman dukes descended from Norwegian/Orkney royal houses, so maybe he has some claims up there too
As he has no children, his heir is his brother Maximilian and then the latter's daughter Sophie, hereditary Princess of Liechtenstein.
So...King Francisco de Portugal, e Infante Massimiliano, e Infanta Sofia, future Sofia Ia, Rainha de Portugal e Algarves.
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I have researched Catherine de Medici's pedigree time and time again and have had difficulty ascertaining where exactly she derived her claim from. I read this first in a book, some years ago, but the book did not give it much attention, only a few sentences: basically, she put forward her claim but was ignored given the existence of more popular Portuguese claimants (junior branches of Avis and royal bastards), Duke Ranuccio of Parma and King Philip of Spain.
All of Catherine de Medici's royal and noble blood comes through her mother, Madeleine de la Tour d'Auvergne, a cousin of the French royal house, since her father Lorenzo de Medici, Duke of Urbino, was basically of peasant blood. However, its quite hard to trace back all of the de la Tour d'Auvergne family and the families they married into, one just ends up getting lost in a huge maze of French nobility...and not every grandfather, grandmother, great-grandfather, etc, of everybody the de la Tour d'Auvergne's married into are on wikipedia.