When Alexander the Great faced the Persian King Darius III on the battlefield and Darius tried to forge a pact with Alexander, Alexander refused by calling Darius the usurper and not the true Persian King. Alexander had a good point even if it may have just been an excuse not to bargain with Darius. Darius I, Cyrus, Xerxes and all the other Persian Kings for hundreds of years up to that point were from the same family. Darius III took the crown only after the remaining brothers in the original Persian line were murdered.

(The Great Courses – The Persian Empire)