There is no doubt that both Huck and Jim fell for the stories about the Duke of Bridgewater and the late Dauphin, Louis the 17th, in Mark Twain's novel, The Adventures of Huckleberry Finn. When the duke revealed his true identity, 

    Jim's eyes bulged out when he heard that, and I reckon mine did, too...
    Jim pitied him ever so much, and so did I.

Then, when the older man could no longer remain silent, and told the other three that he was the "rightful King of France,"

... we was so sorry--and so glad and proud we'd got him with us, too... So, Jim and I set to majestying him.

However, Huck was not fooled for long.

    It didn't take me long to make up my mind that these liars warn't no kings nor dukes at all, but just low-down humbugs and frauds. But I never said nothing; never let on; kept it to myself; it's the best way; then you don't have no quarrels and don't get into no trouble... If I never learnt nothing else out of Pap, I learnt that the best way to get along with his kind of people is to let them have their own way.

Of course, Huck soon found out that this pair of liars were nothing but trouble, and it took several close calls and their eventual tar-and-feathering to rid Huck of their company.