Historical accounts about Yuan and his fellow coup leaders generally referred to them as the "five princes," and, as their titles were restored after Emperor Ruizong's ascension, they were generally considered to have been restored to their princely ranks, although Yuan's biography in the Old Book of Tang quoted an edict of Emperor Xuanzong's referring to him as the Duke of Nanyang, and therefore it is not completely clear whether Yuan, posthumously, was formally referred to as a duke or a prince. See Old Book of Tang, vol. 91.[1]
