The Nights of Lucretia Borgia.

Federico, a virtuous nobleman from an impoverished family, is brought into service by autocrat Cesare Borgia. His promiscuous sister Lucrezia seems to have an amorous interest in Federico and wants him as her lover though Federico is in love with Diana, the Duke of Alva's daughter, whom he has saved from being raped. When he learns about Diana's feud against the Borgia clan, he becomes aware of their infamous deeds.