I'm reading Henry Kissinger's A World Restored right now. As the Allies are winding up the war, Kissinger says that Metternich views either Napoleon or the Bourbons as legitimate rulers of France, and while Metternich has preferences, either one would be an acceptable ruler after the war.
Metternich is an uber-conservative servant of the Hapsburgs, so I'm wondering why he would even consider Napoleon a legitimate claimant to the throne of France when the House of Bourbon still has claimants. How did Napoleon get legitimacy even though he was the result of a massive and unprecedented revolution?
Important to know is that while Metternich was very conservative, he was also very aware of the power of Napoleon. He never fully supported Napoleon but acted in support of him due to the defeats of Austria at the hands of Napoleon. However in 1813, once the tables were turning, Metternich was important to Austrian diplomacy with the Allies. Further, Napoleon saw Metternich as the problem within the Austrian Empire, swaying "Papa François" from Napoleon (From a letter to Marie Louise).
However Napoleon gained legitimacy from the people through plebiscites that placed Napoleon as Consul for Life and Emperor. The plebiscites are generally accepted as legitimate with some tampering in voting records only to make a clear victory (70% in favor) to an adulterated absolute victory (95+% in favor).