Following on from this thread from 2013 (
https://www.alternatehistory.com/forum/threads/king-for-a-day-duke-for-a-lifetime.296626/), how different would things be if Duarte (Edward), Duke of Guimarães (
https://en.wikipedia.org/wiki/Infante_Duarte,_5th_Duke_of_Guimarães), had not died in 1576?
Firstly, the Portuguese Empire might not come under as much pressure from the English and Dutch as they did IOTL. The Spanish Armada might not sail, at least not in the it did IOTL. Being a Catholic, Duarte would be opposed to Queen Elizabeth in principle, and, through his descent from John of Gaunt, might have had a claim to the English throne. However, if Sebastian still dies the way he did IOTL, the Portuguese might be leery about future military actions.
At first I wondered if Cardinal Henry might still become king after Sebastian's death, but then I thought that, if Duarte was still alive, the Portuguese nobles might not be so desperate.
On the old thread, the general concensus was that Duarte II might marry one of Philip II of Spain's daughters - Isabella Eugenia Clara or Catherine Michelle. Personally, I'd be more inclined towards Catherine Michelle, and not just because of her portrait. It was mainly this:
Isabella Eugenia Clara was Philip II's eldest daughter, and, given Philip II's luck with sons,
might have been in a position to become his heir. The Portuguese might have been fine with a Spanish king (at least in the beginning), but the Spanish might not have been receptive to a Portuguese king.
I'm not suggesting that Diego or OTL Philip III would both die. I'm just saying Philip II might have considered it a possibility. That, and there's the Hapsburgs' tendencies to keep their domains "in the family".
Finally, there's discussion on what sort of person Duarte was. He was supposedly one of the most influential nobles during the reigns of John III and Sebastian, had supported Sebastian's betrothal to Margaret of Valois, and he had accompanied Sebastian's first trip to Tangiers in 1574, so he was probably no stranger to battle. He also seemed to have a certain prestige due to being one of the last legitimate male descendants of King Manuel of Portugal, which seemed to be part of the reason for Sebastian's jealousy of Duarte.
Any other thoughts?