Queen Maria II of Portugal was originally betrothed to her uncle, D. Miguel I, when he renegged on that promise, they set about finding another husband for her. The choice fell on Prince Auguste de Beauharnais, Duke of Leuchtenberg because of his lack of familial connections - his mother was a Bavarian princess, and his father was Napoleon's stepson.
Unfortunately Auguste married the queen, fell ill and died, and the Leuchtenberg title passed to his brother Maximilian, who was married to a daughter of the Russian Emperor.
Around the same time that Auguste and Maria got married, her father was marrying as his second wife, Auguste's sister, Amelia. They were slightly more successful (if it can be regarded as that) in the matter of producing a child - a tubercular daughter, the Infanta Maria Amelia of Portugal and Brazil.
Maria Amelia was betrothed to Archduke Maximilian (yes, the same Max that was shot as Emperor of Mexico), but died before the wedding could take place.
Now here are my questions: 1) What if Auguste hadn't died, and had had children with Maria; 2) what if Pedro I of Brazil had had a son with Amelia, would he maybe partition the empire - Portugal to his son from his first marriage, and Brazil to the son by Amelia? or some other compromise; 3) What if Maria Amelia and Max had married? Would there be any significant changes to his life i.e. would he still go to Mexico and be shot or would he be just another Austrian Archduke bouncing around the Empire, would he have children etc