When learning about ancient history, such as that of pre-Roman Egypt for example, you might get a passing reference from the teacher about the occasional incestuous marriage among the pharaohs here and there. But the Ptolemaic Dynasty took this to the next level. Let's have a look at this handy chart
Of special note is that Ptolemy VIII was, for a time, married to both his sister AND his niece (who herself was the daughter of Ptolemy's sister/wife and their brother). Also, the Ptolemies spent a whoooole lot of time murdering one another - parents murdered by their children, children murdered by their parents, uncles, or aunts, and so forth. Interesting times, to say the least.