After ditching the Countess of Castiglione, Napoleon III's next mistress was Marie-Anne Walewska. This gave gave an extra frisson to the discussion of foreign affairs - she was the wife of Alexandre Colonna-Walewski, the emperor's foreign minister. Not only that, but Walewski was an illegitimate son of Napoleon Bonaparte.
Napoleon III was not brilliant at hiding his affairs. On a train, his wife was in a different carriage talking to another passenger. The jolting train caused the door to the adjoining carriage to swing open and the empress saw, Napoleon III "straddling” another woman, “kissing her on the mouth and plunging a hand onto her breast.”