I read it a very long time ago, so my details are a little scarce.
The story was about a kid who had psychic powers. He is invited onto a talk show or something similar, and asked what his prediction for the world is. He foretells of all the wars ending, everything being wonderful and hunky dory; basically predicting that the world will be one big Utopia. The citizens of Earth all rejoice and go around loving their fellow man, etc, etc.
Turns out that the kid had lied about his predictions, and that the future was much more bleak (and immediate). Apparently the sun is about to go supernova the next day, and he wanted to give everyone one day of happiness as their last day on Earth.
Does this sound familiar to anyone?