The title of Duke of Guarda (in Portuguese, Duque da Guarda) was granted by a royal decree dated from October 5, 1530, by King John III to his younger brother, Infante Ferdinand. Some authors say the Infante was also made Duke of Trancoso (in Portuguese, Duque de Trancoso) at the same date (according to Arquivo do Conselho Nobiliárquico de Portugal, Vol I, 78). However, the majority of historians maintain that the Dukedom of Trancoso did not exist, and that the confusion comes from the fact that Infante Ferdinand (Fernando, in Portuguese) was also Lord of Trancoso.