how did prospero affect antonio's rise to power?

Prospero reveals to Miranda that Antonio is his brother, and that he was once the rightful Duke of Milan, a position Antonio now holds. Antonio usurped Prospero's estate and wealth while Prospero became increasingly "rapt in secret studies" and oblivious to his brother's machinations; and in order to take Prospero's title as well, Antonio arranged to have his brother Prospero and Prospero's daughter Miranda killed secretly.