Stephen Hawking is ''incredibly sharp and witty''.

The theoretical physicist is the subject of new film 'The Theory of Everything' and one of the stars of the biopic, Felicity Jones - who plays the scientist's ex-wife Jane Wilde - was struck by the professor's sense of humour when they met prior to shooting.

She shared: ''He's so incredibly sharp and witty. And really, it's just an extraordinary, extraordinary love story and it's an absolute privilege that they let us tell this story.''

The film focuses on the love story of Stephen and Jane, who he was married to from 1965 to 1995, and Eddie Redmayne - who plays the professor - says the storyline is ''incredibly intimate'' and he was determined to land a role in the movie.

The 32-year-old actor explained: ''When I heard of the film I thought it was going to be a biopic of Stephen's life, but what I read was incredibly intimate.

''It's a passionate love story about two extraordinary people and when I heard that James Marsh was directing, it was too tantalising a prospect not to pursue.''