In my first game, playing as Sicily, i had one interesting king, who had some 10 children, including a bastard daughter. When he became old (he was +60 years old), long after i had broken relations with the mistress, i got the message
"I think Constantia might fancy me", the woman was his own bastard daughter... and i accepted. The worst part was when he had a son with her... who was simultaneously his own grandson O.O
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Also, this one might be more common, but i still find it funny. When playing as William the conqueror, i married my grandson to an Abyssinian princess, just for the lulz. Due to sheer luck, he became the next king... and his son (Henry) and grandson (Roger) have the portraits of muslim rulers...
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