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.
Finally, others say he was Duke of Guarda and Trancoso (a joint dukedom).
Whatever the truth of this, it is certain that Infante Ferdinand was the sole bearer of the title of Duke of Guarda.
But when the Infante's marriage was announced, the Marquis of Torres Novas (who later became the 1st Duke of Aveiro) declared that he had already secretly married the rich heiress. The scandal in the Court ended when King John III ordered the imprisonment of the marquis for several years, allowing the celebration of the Infante Ferdinand's marriage.
The marriage was short but apparently happy: the couple had two children (a boy and a girl), who died at a very young age, before their parents.
"Nobreza de Portugal e do Brasil" - Vol. I, page 385. Published by Zairol Lda., Lisbon 1989.