The Mysterious Island
As noted above, Hetzel and Verne generated a sequel of sorts to this novel: "L'Île mystérieuse" ("The Mysterious Island", 1874), which attempts to round off narratives begun in "Twenty Thousand Leagues Under the Seas" and "Captain Grant's Children", aka "In Search of the Castaways". While "The Mysterious Island" attempts to provide additional background on Nemo (or Prince Dakkar), it is muddled by irreconcilable chronological discrepancies between the two books and even within "The Mysterious Island" itself.