Actor Will Smith (L) and Mongolian sumo wrestler Asashoryu laugh on the red carpet during a Japan premiere for the film "Hancock" in Tokyo August 21, 2008. [Agencies]

Will Smith thinks being physically fit is the key to happiness. The actor - who had to get in great shape for a number of film roles, including 'I Am Legend' and 'Ali' - thinks a healthy body equals a healthy mind.

He said: "I feel like everything in my life depends on physical conditioning. I love eating sweets and everything, but I think the quality of my parenting, the quality of my relationship with my wife - it is all based on being on great physical condition. "I believe it's the beginning of finding true happiness." Meanwhile, Will is to star in a prequel to 'I Am Legend'.

Director Francis Lawrence has confirmed the 'Men in Black' actor will reprise his role as Robert Neville - though he admits they haven't yet worked out a plot yet.

Francis said: "Absolutely, we're actually trying to crack a second movie. We're trying to figure out some ideas for it, but yes, it would be a prequel."