Man, look at Christian being all beautiful! Christian loved to play football, watch television, and rummage through drawers, just like a human being! After a year he grew too big to be kept as a pet and John Rendall and Ace Berg (the two friends who bought Christian) tried to figure out what to do. Through a stroke of luck, they managed to get in touch with George Adamson, who spent his time rehabilitating lions raised in captivity back into the wild, among other lion-related things.
Christian was sent to Kenya with George Adamson to join a pride of lions. Despite an initial struggle (Christian knew nothing about lion etiquette), he adjusted beautifully and had lion cubs of his own and disappeared for a long time. A year later, when John and Ace contacted George Adamson to get an update on how Christian was doing and whether they could visit, Adamson warned John and Ace that visiting would be completely futile; Christian had adjusted to a new way of life and wouldn't remember them at all. John and Ace flew to Kenya anyway.
Here's a video of them in Kenya, a year after releasing Christian into the wild. Watch Christian's jaw drop when he recognizes them:
There is a movie (Christian the Lion at World's End) and a book based on Christian's story. I think it was released on DVD in 2006.
Credit to Deb for introducing me to the video (& story) and this newspaper article for the info & photos. I definitely recommend the article; it's freakin' called "Christian, the lion who lived in my London living room" (!!). Are you sold?