Balsamo The Magician
More of a short story I didn’t realize that Balsamo was a real person: https://en.wikipedia.org/wiki/Alessandro_Cagliostro
Also the history of Madame du Barry: https://en.wikipedia.org/wiki/Madame_du_Barry
The book was short, or a long short story which only began to set up the character and events. Apparently it is part of a 3 book series that I have to track down the next two parts. This has the usual Dumas attention to historical detail but also seems to be dabbling in more fantasy with Balsamo and maybe even comedy.