Prince Louis Napoleon was the son of Hortense de Beauharnais, the daughter of Josephine de Beauharnais and therefore the stepdaughter of Napoleon I. His "father of record" (but quite possibly not his real father) was Louis Bonaparte, Napoleon's younger brother.
He was elected as president in 1848, following the abdication of Louis-Philippe. He was forbidden by the constitution from standing for a second term, so he arranged a coup d'etat in 1851, and took the throne in 1852 as Napoleon III.
His periods as President and Emperor are known, respectively, as the Second Republic and the Second Empire.
The Second Empire collapsed as a result of the Franco–Prussian war of 1870–1, and was replaced by the Third Republic (which lasted until 1940). After a period of exile in Germany, Louis Napoleon and his family settled in Chislehurst, Kent, and he died there in 1873.
"Napoleon II" was the son of Napoleon I and his second wife, Archduchess Marie Louise of Austria. He was recognised as Emperor for 15 days, from his father's abdication (22 June 1815) until the entry of the allied forces into Paris (7 July). He was only 4 years old at the time. He lived thereafter as a virtual captive in Austria, and died of tuberculosis in Schönbrunn Palace (aged 21) in 1832. It's only Bonapartists that refer to him as Napoleon II; but the next Bonaparte to claim the title of Emperor took the name Napoleon III in deference to him.
© Haydn Thompson 2017