With this in mind, I was wondering about other living royals with potential claims to two or more thrones. Case in point: Karl Friedrich, the present-day head of the princely house of Hohenzollern-Sigmaringen. According to the 1923 Romanian constitution, he would also be the rightful king of the country, if it were still a reigning monarchy.
Aside from these claims, he could potentially claim headship of the royal house of Saxony, if the principle of Ebenbürtigkeit were strictly defined and enforced, in accordance with pre-World War I standards. After all, the Saxon succession is semi-Salic; and indeed, until his death in 1987, Prince Johannes of Saxe-Coburg and Gotha was groomed as the rightful heir of his uncle, Margrave Max Emanuel. The reason was that he was the son of his sister Mathilde, the only princess in the family to have married in accordance with existing house laws.
As it was, his tragic death in an accident left the dynasty without a clear heir; so Margrave Max adopted a nephew through another sister (Anna, who married a prince of Gessaphe) as his heir. But the claim of Alexander today is questioned and contested, on the grounds that he does not meet the *equal birth* requirement. In this, his situation is comparable to that of the Grand Duchess Maria Vladimirovna of Russia today, in her claim to headship of the Romanovs.
Her case essentially hangs on the thread of *equality* -- whether or not her mother (Princess Leonida of Georgia) met the dynastic standards of the Russian imperial house. If it fell apart, the claim to headship could potentially fall to the descendants of her aunts, the sisters of Grand Duke Vladimir Kirillovich: after all, both married in accordance with pre-World War I standards. Or at least the younger one (Kira) did ...
Bearing this in mind, the Saxon case could also be settled in additional lines of descent through females, since the dynastic male line is clearly extinct. The next person coming to mind, then, would be Princess Margaret Karola -- the eldest daughter of King Friedrich Augustus III, and aunt of Margrave Max. As it is, Karl Friedrich is her grandson, being the eldest son of her eldest son.
So that would make him into the potential heir to three thrones. Now: there is nothing unusual about having two claims (look at the Duke of Bavaria, who happens also to be the Jacobite pretender).
But who else has three or more potential claims? Can anybody name additional examples? If it came to that, I'd be interested in other examples of royals with two claims ...