Sui generis
Sui generis (; ) is a Latin phrase that means "of its (his, her, their) own kind; in a class by itself; unique."
Prince du sang
A prince du sang (, Prince of the Blood) is a person legitimately descended in dynastic line from any of a realm's hereditary monarchs. Historically, the term has been used to refer to men and women descended in the male line from a sovereign, although as absolute primogeniture has become more common in monarchies, those with succession rights through female descent are more likely than in the past to be accorded the princely title (e.g., Belgian Royal Family).