Benedict Cumberbatch is a lovely dude, says Keira Knightley

'Atonement' star Keira Knightley has praised the compassion of co-star Bendedict Cumberbatch and commended his incredible rise to fame.

The pair star in biopic The Imitation Game, in which Cumberbatch plays trailblazing mathematician Alan Turing, who helped break the Enigma code during during World War II. Knightley, 29, plays close friend Joan Clarke, who later became engaged to him, reported Harper's Bazaar.

"Benedict is a very good dinner companion: always interested and interesting, up on politics and the news (so he's got an opinion) and always ready with a story, although occasionally you have to pin him down to one subject because he tends to veer off in all directions," Knightley said.

Asked why Cumberbatch makes such a caring friend, Knightley said, "There have been moments in our friendship when I have been going through tough times and he has been right there, taking me out to dinner, coming round to the house, being the one who listened. I appreciate that hugely."

The actress also spoke about the 'Sherlock' star's meteoric rise to fame, adding: "He is really enjoying his success. He is 38, and has wanted this for such a long time and has worked so hard. Most importantly, his love for acting is something I haven't seen in anyone else. He has found the one thing in life he is singularly passionate about and he is making the most of it."