So I'm a couple of days late, sue me.
When Sebastian I decided that it was a smashing idea to go off to Africa and fight the Muslims, he forgot one teensy, weensy, insignificant detail. He was single and childless.
So when he went missing, the result was one gigantic problem which I'll sum up. Phillip II of Spain had a large claim to the throne, but Catarina, the Duchess of Bragança had a bigger one. He, however, had big armies.
Well, the portuguese nobles didn't forget Catarina's claim, and after 60 years of Spanish rule, they were a bit ticked.
Catarina's grandson didn't want the throne, but his wife did. When he was undecisive about the whole plot, she had their youngest daughter brought to them, and asked him if he was going to deny their daughter the right of being an Infanta.
On December 1st of 1640, the nobles raised up arms and headed to the Terreiro do Paço, where the Vice-Queen of Portugal, the Duchess of Mantua and her lover, Miguel de Vasconcelos had set up shop.
He was found hiding in a closet, dragged out, stabbed, thrown out of a window and torn to pieces by an angry mob, courtesy of the Duke.
In comparison, the Duchess could count herself very lucky. She was abducted and informed that if she didn't command all Spanish military posts in Portugal to surrender themselves, their officers would find themselves a head short. She accepted and seven days later the Duke of Bragança was crowned João IV of Portugal and founder of the Dinasty of Bragança.
I'm sure you can guess who the daughter was.