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You don't say. Justin Bieber tested the gullibility of fans and the media on Christmas Eve when he tweeted -- to instant chaos! -- that he was "officially retiring." A few tweets later, he assured his supporters: "The media talks a lot about me. They make a up a lot of lies and want me to fail but I'm never leaving you, being a belieber is a lifestyle."

"He isn't retiring, clearly," a source close to the "Boyfriend" singer, 19, reiterates to Us Weekly.

"It was a joke and he explained in two tweets afterwards!" Continues the insider: "He is basically poking fun of how quickly news spreads without anyone vetting if it is true or not."

The prank was also a great marketing ploy: Believe, Bieber's second documentary film, hit theaters on Christmas day.