The Theory of EverythingMaking a biopic about still-living people is nerve-wracking stuff, according to the cast and crew of "The Theory of Everything," which tells the story of Stephen Hawking and his wife, Jane Wilde. But when the subjects of the film come to visit the set, the stakes are even higher.

A new featurette about "Theory," premiering today exclusively on Moviefone, depicts just such an occasion, when Hawking and Wilde stopped by the Cambridge shoot to watch the filming of the key May Ball scene.

The Theory of Everything - Steven Hawking Visits the Set

"It was the most surreal experience," says Felicity Jones, who plays Wilde in the film, about seeing the real-life couple on set while delivering her lines. Co-star Eddie Redmayne, who plays Hawking, put it more bluntly, saying he felt "great trepidation" about the experience, but also "wonderful pride" knowing Hawking was watching them work.

For his part, Hawking was quite pleased with "Theory," noting that he was "quite surprised" that a film would be made about him, and praising the "extraordinary" May Ball scene in particular.

Check out the behind-the-scenes action -- and the stunning fireworks show -- below. "The Theory of Everything" is in theaters now.

Photo credit: Liam Daniel/Focus Features