Virginia Oldoini was born to minor nobles in Tuscany in 1837. When she was 17, they married her off to a guy 12 years older than her. But a year later her cousin decided that it would be a lot more convenient to his career and country if Virginia was available to have sex with someone else. Namely, Napoleon III.
See, at that time, what we now call Italy was a bunch of smaller countries, and Virginia’s cousin was part of the group that wanted them to unify. He took one look at his hot, young, close relative and realized the best plan was to get her to cheat on her husband with Napoleon and hope some political pillow talk could turn the tide. Because 19th-century Europe was apparently an alternate-universe Game Of Thrones, complete with a short guy and creepy family relationships. Virginia managed to become the emperor’s mistress for over a year, and shortly after it ended he sent troops to unite the peninsula.