BERLIN - Knut the superstar polar bear turns 2 on Friday looking nothing like the button-eyed ball of white fluff who captured hearts around the world.

The star of the Berlin Zoo is a fully grown bear with yellowish fur who, at 440 pounds, has grown too big for his enclosure. Worried fans are lobbying for him to stay, but zoo officials say he will have to move if they do not build a new enclosure, which appears virtually impossible due to lack of space.