On January 26, 1531 there was an earthquake that killed 30000 people in Lisbon and Santarém.
What if the King of Portugal John III, along with his wife Catherine of Austria and his only daughter Maria Manuela died in this earthquake?
Consequently the couple dying this year, Sebastian I, his grandson, and future King of Portugal would not exist, and Philip II of Spain would never have married Maria Manuela, there would be no heirs to the throne of the couple.
Which of John III's brothers could come to take the throne?
What would be the consequences of this scenario?