In 1650, John IV of Portugal, fearing a possible defeat in the war against Spain for the Portuguese independence from the Iberian Union, sent the father Antonio Vieira in a diplomatic mission to Rome. He wanted to offer to the Spanish the possibility of a marriage between his son, Teodosio, and the Princess of Asturias, Maria Theresa of Spain, until now the heir of the Spanish throne. If Philip had no more male heirs she would be the queen, and married to Teodosio their heirs would united both the Habsburg and the Braganza claim to Portugal.
With this marriage, John IV wanted to keep the Iberian Union and put an end to the expensive war he needed to fight. He even offered to the Spanish his own abdication on behalf of his son if Philip IV didn't accept John as king.
However, the Spanish didn't have any reason to accept it. Portugal could still be defeated, and Maria Theresa would be more useful for other diplomatic marriages (as she was IOTL with France) and Philip could still have a male heir. Also, the news that the Portuguese tried to help a rebellion agains the Spanish in Naples didn't help John's plan.
But how could Philip IV had accepted that? Would the Portuguese accept that (their own king arranging the reunion with Spain)? And assuming that Philip IV doesn't have a healthy male son as IOTL, how would be an Iberian Union under the House of Braganza?
With this marriage, John IV wanted to keep the Iberian Union and put an end to the expensive war he needed to fight. He even offered to the Spanish his own abdication on behalf of his son if Philip IV didn't accept John as king.
However, the Spanish didn't have any reason to accept it. Portugal could still be defeated, and Maria Theresa would be more useful for other diplomatic marriages (as she was IOTL with France) and Philip could still have a male heir. Also, the news that the Portuguese tried to help a rebellion agains the Spanish in Naples didn't help John's plan.
But how could Philip IV had accepted that? Would the Portuguese accept that (their own king arranging the reunion with Spain)? And assuming that Philip IV doesn't have a healthy male son as IOTL, how would be an Iberian Union under the House of Braganza?