1. Un príncipe perdido, un otro príncipe adquirido (1497-1498)
~ Un príncipe perdido, un otro príncipe adquirido ~
The Iberian Peninsula c. 1497-1498
El Bautismo de Don Juan - 1478
Fearing for their daughter’s well being and anxious to fulfill the royal marriage demanded by Treaty at Alcáçovas in 1479, the Catholic Monarchs urged the Infanta to accept the hand of Manuel, who would settle for no other bride. Despite her intense reluctance, Isabel consented to her parents’ wishes and agreed to marry Manuel. Finding her thin build graceful and her knowledge of Portugal charming , Manuel quickly became enamored with his new wife and gradually coaxed her out of her grieving shell and back into relatively good health and happiness. 
El puente de Alcántara
However, as one marriage flourished, another found itself dying on the vine. Don Juan, the Prince of Asturias and heir presumptive to the realms of Aragon and Castile, newly wed and installed in an administrative position in the city of Salamanca, was bedridden with a high fever less than a month after his sister’s departure. It was decided that Isabel would stay in Portugal for her daughter’s wedding while Fernando would hasten to Salamanca to attend to their eldest son. When Fernando arrived, Juan had grown extremely pale but remained articulate and aware. Juan told his father that he had accepted his impending death, but Fernando begged him not to lose hope. Nonetheless, Juan’s condition worsened irreversibly, and he died a mere two weeks later. It was, in fact, a miracle that Juan had survived so many years given his frail constitution, yet his death still brought deep sorrow to his parents - as well as an acute sense of dread concerning the future of Castile and Aragon. The once secure succession under Juan that Fernando and Isabel had so carefully organized was in shambles, finally torn up at the root when the child of Juan and his Habsburg wife Margaret was miscarried a few months later. When Juan’s body was laid to rest, the writer Pedro Mártir captured just how dour this development had rendered the future of Castile and Aragon: “There was buried the hope of all Spain.”
Yet hope remained. Refusing to let despair sink in, much less hamper their characteristic vigor, the Catholic Monarchs immediately set about re-establishing the line of succession through their eldest daughter Isabel. While Manuel was careful to ensure the continued separateness of Portugal from Castile, he and his wife received the oath from the Castilian Cortes in Toledo on March 16th of 1498, and would be invested with the titles of King and Queen of Portugal and Castile following the deaths of Isabel and Fernando - although Manuel and the Infanta would have proprietary rights only to their respective inheritances. The problem of succession in the kingdom of Aragon would be a trickier matter. By Aragon’s ancient constitution, it was strictly forbidden that a woman ever bear the scepter, thus eliminating the infanta from her father’s inheritance - that is, unless she could produce a male heir.
A united, Christian Spain had been the grand ambition of practically every Spanish prince and potentate since the demise of the Visigoths, yet it had become much more desperately hoped for over the course of the 14th and 15th centuries, especially in regards to the peace that would accompany it. The desire for peninsular peace was reaching a fever pitch following the Castilian civil war  - having occurred a mere twenty years prior to the death of Don Juan and remaining fresh in the Iberian mind.
The inheritance awaiting the Infanta's child
(Not shown: Aragon's Italian possessions or Portugal and Castile's American/African possessions)
With the possibility of an Iberian union in the hands of someone as delicate as the Infanta, the courts of the Iberian kingdoms deemed the Trastámara line all but extinguished, the Infanta’s physical inability to survive a pregnancy or produce anything but a stillborn considered foregone conclusions. In fact, news of the Infanta approaching the critical stages of her pregnancy were greeted not with hopeful anticipation by the grandes and common folk, but with solemn, funerary vigils. Such predictions were not helped by the attitude of the Infanta, who frequently proclaimed that she knew she would die in childbirth, and who kept the viaticum and monks ready to dispense Last Rites close at hand.
Even though she barely made it through the labor with her life, the Infanta produced a healthy male heir against all odds . This boy would be named Miguel - a break with tradition, as none of his predecessors had borne the name - and would promptly be given the epithet “da Paz” by his father. The dichotomy of this nomenclature - being both deemed “of peace” and named after Michael, the warrior archangel and bringer of the sword - would prove to be telling.
The Infanta’s recuperation would take nearly eight months, leaving Miguel almost entirely in the care of his wet nurse. Yet the Infanta would indeed recuperate, and the son she had birthed would live for many more decades. While Isabel and Fernando considered the union of Spain of greater importance than dynastic squabbling, the inheritance of Castile and Aragon - Trastámara possessions - by a different house (no matter how close in relation) was a matter somewhat distasteful to the Catholic Monarchs and smacked of Portuguese dominance to Castilian and Aragonese grandes. Manuel and the Catholic Monarchs therefore reached an agreement in the the Treaty of Montehermoso, signed on the 2nd of November 1498, which declared Miguel to be bilineal - of the house ‘Avís y Trastámara.’
Montehermoso moderno en Extremadura de España
1498 was to be a seminal date in Spanish history - the last year in which the kingdoms of Portugal, Castile, and Aragon would be fully independent of one another. This solidarity would be much needed, as Spain’s situation became one of both ever-increasing potential and constant threat all within a very short space of time during 1498: to the far west, the city of Santo Domingo was officially founded on Española under the supervision of Cristóbal Colón; to the immediate east, despite a coalition led by Fernando of Aragon having just driven the French out of Italy, France’s young king Charles VIII had died unexpectedly  and was replaced by the older, more pugnacious Louis of Orléans, now Louis XII, who began to eye the Mezzogiorno; and around the Cabo da Boa Esperança, Vasco da Gama and his crew landed at Calicut, becoming the first Europeans to reach India by sea. After 1498 would begin a ‘siglo de oro’ for Spain - while Europe would marvel at the accomplishments of a Spain mostly disinterested with its home continent, the rest of the world would begin to feel the full weight of an empire with a zeal of purpose and a global reach unmatched in history.
 Manuel's predecessor.
 The Infanta Isabel had spent three years of her youth in Portugal. The Infanta was also the favorite daughter of her mother, who also spent a great deal of her youth in Portugal and had a Portuguese mother.
 This is a semi-PoD. The Infanta never really recovered physically or emotionally from her lost love Afonso.
 In which Portugal was essentially Castile's opposition.
 This is more or less the PoD. The Infanta died during childbirth and Miguel died before he reached the age of 2. Here, both survive.
 He suffered a cerebral hemorrhage after hitting his head on a door frame on his way to a tennis match, which - as far as death goes - is pretty hilarious.