Napoleon II (1811-1832) was the only son of Napoleon I and cousin of Napoleon III. You haven't heard of him because officially, he was a bastard Austrian Habsburg and died before he had a chance to be like his dad and conquer France.
Napoleon II was Boney's son by his second wife, Marie-Louise 'sticky Viennese schnitzels' Habsburg, daughter of the Emperor Francis. The Corsican adventurer wanted to 'marry up' in Monarchial terms and had dumped first wife Josephine for 'failing to give me a boy'. Marie-Louise was actually his second choice after the Russian Romanovs refused to have a coarse peasant as a brother-in-law. It was simple as that.
King of Rome
Napoleon Junior was born as a King, King of Rome to be exact which his father dispensed on his son by way of a birthday present. Napoleon Fils never got to see his new home or the people there because three years later, Napoleon I abdicated and recommend the French take on a three year old baby as their new ruler. So having cut off one baby-man's head off in 1793 (Louis XVI), French politics had come full circle. The French said 'Oiu!' but Allied leaders of Great Britain, Austria, Prussia and Russia said this was a terrible idea. The Austrians promptly reclaimed Napoleon II as one of theirs and the boy was packed off to Vienna to learn German.
Duke of Reichstadt
In 1815 Napoleon came back to France and said he 'was back in control' - legally forgetting he had given up his throne to his son the year before. Whatever long term plans Napoleon I had for himself were cancelled after the Battle of Waterloo. So he re-abdicated in favour of Napoleon II again and then tried to flee to the USA for protection. Napoleon got the one way ticket to St.Helena whilst Napoleon II was deposed again and obliged change his name to 'Fritz Bratwurst' and to never speak of his father again. Napoleon II/Fritz was given the title of 'Duke of Reichstadt' which was a pig farm outside Salzburg.
The boy grew up to a thin faced, weak chinned man with little to zero charisma. His mother stayed away from her son, preferring to live in Italy as the ruler of her statelet as the Duchess of Parma Ham and Cheese Pizza with Anchovies. Marie-Louise hadn't wanted the marriage but she produced the required male child for Napoleon and cleared of when the emperor went for a long march to Moscow.
Napoleon Junior got more noticed when his father died in 1821. To avid Bonapartists Napoleon II was their rightful emperor. They hoped to restore the Bonaparte family. In 1830 there was a new revolution in France which saw the departure of the restored Bourbons. If only Napoleon II could escape Austria and come to France...but nothing happened. Nappy Deux (or should that be Nappy Zwei) remained in Vienna and stopped eating.
He started to grow thinner and thinner and then started to revert into speaking French, which annoyed his Austrian family. Officially Napoleon II died of a nasty rash in his groin, suggesting he had inherited something else from his father besides a name. This grew septic and Napoleon died.
Napoleon II died unmarried and a virgin in 1832. It was a bit of an expected fate of a great man of history. Sons and daughters of 'the greats' never live up to their family forbears. Alexander the Great's son was murdered before he reached manhood whilst Oliver Cromwell's son Richard Cromwell turned out to be a flop.
Napoleon died in Vienna but in 1940 he was given the chance to see his father again in Paris. His tomb was moved to the same building where Napoleon I lay buried. So that's a sort of happy ending except of course they were both dead and small talk was out of the question. On a happier note, Napoleon II's mother got to marry twice more and lived till 1847, leaving descendants. Napoleon II remains unknown and nothing dramatic or tragic has been written about him.