I found the following story on Futility Closet's blog here.
In August 1857, 13-year-old Narcisse Pelletier left Marseilles as a cabin boy aboard the Saint-Paul, a three-masted ship bound for Sydney. The ship struck a reef in Papua New Guinea, and Pelletier was feared dead. His parents mourned him for 17 years, until July 21, 1875, when they received this letter:
papa mama i am not dead i am living narcisse I was on board the saint paul of bordeaux I had been shipwrecked in the rock of the savage of the island the chinese in the island stayed and died killed I came in a little boat to an island of savages I had looked for water to drink the captain left in the little boat I looked for water in the woods I stayed in the woods I then see the savages who live on its coast come who had found me the savage gave food and drink he did not kill I give my hand he did not hurt me I stayed in the wood for a very long time I was almost dead I had o great hunger and great drink I was in a lot of pain
Pelletier explained that after the sinking he, the captain, and the surviving crew had crossed the Coral Sea in an open boat to Cape York in northern Australia, where Pelletier was somehow left behind and discovered by a community of aborigines, with whom he lived until he was discovered that year by a landing party from pearling boat. He returned to France, where his thanksgiving mass was celebrated by the same priest who had baptized him 32 years earlier. He married and lived quietly as a lighthouse-keeper until his death in 1894.