This story might seem a bit unbelievable, but it's true. You can check it's validity at various sites around the web, and the one that you ALWAYS check says it's true, too. Snopes says the story is true...and if there's one entity on the web that you can trust about urban legends and such, it's Snopes.
Christian the Lion...This first one is a brief video showing the highlights of the first part of the reunion.
This second video shows a bit more of it, and is a bit more professional in quality as far as the production is concerned.