Napoleon's sister Pauline, the Messalina of the new empire, may have had an incestuous affair with her brother, who boasted countless mistresses. Napoleon had an affair with Hortense Beauharnais, then promptly married her off to his brother, Louis Bonaparte, king of Holland.
By this time she was pregnant with Napoleon's child. Thus Hortense became both Napoleon's sister-in-law and the mother of his child, to whom he was both father and uncle.