Hawking's powerful presence was felt by the audience at the ArcLight Hollywood as Redmayne, costar Felicity Jones and producer Lisa Bruce discussed the renowned physicist during a Q&A on Thursday, following a showing of their film at Variety's Screening Series.
Redmayne recounted his nervous first encounter with Hawking with as much giddy enthusiasm as one would imagine likely characterised the meeting itself.
When asked by Variety awards editor Tim Gray if he got the chance to ask the scientist intimate details about his life, Redmayne said he didn't, but what little Hawking was able to communicate changed the course of the film.
"In the three hours that I spent with him, he may have said eight or nine sentences, and some of them were wonderfully specific about, for example, his voice," Redmayne said.
Because Hawking can now only communicate with an eye tracker, Redmayne explained that it can take up to eight minutes for him to say something in live conversation.
Hawking told Redmayne that his speech was extremely slurred following his amyotrophic lateral sclerosis (ALS) diagnosis, which prompted screenwriter Anthony McCarten to further emphasise the cosmologist's vocal decline and weave into the script scenes of his wife Jane (played by Jones) translating on his behalf.
But it wasn't what Hawking said that stuck with Redmayne; it was his aura.
"Really what I gained from that experience with him was more what he emanates: It was this extraordinary, incisive weight, a formidable sense of humor and most of all, a sense of mischief," he said. "I described it as a Lord of Misrule quality. Even though it's difficult for him to communicate, he completely runs the room and you can really feel his power."
Redmayne chatted with Hawking just before the physicist saw "The Theory of Everything" for the first time, and admitted that he was anxious to know what Hawking thought of the piece. Hawking's now infamous reply speaks volumes about his sense of humor.
"I said, 'Stephen, I'm really nervous, but I hope you enjoy it. Let me know what you think,'" Redmayne told the audience. "And he took a while to write his response and he said, 'I will let you know what I think -- good or otherwise.'"
Hawking was moved to tears after watching the film, but didn't express his feelings verbally.
"When the film ended and the nurse came over and was mopping his eyes, it's an indescribable moment really," Bruce said. "Because he's not typically known for that and he was really quite moved."
Jones said he made one comment about the film.
"Someone said, 'Oh, what did you think?' He said, 'Broadly true.' Which is the true sort of two sides of Stephen Hawking, which is the wit and the unsentimentality, but also the profound man."
But it was true enough for Hawking to lend his voice, which he's copyrighted, to the drama.
"After seeing the film, he offered us his voice, and it totally lifted and somehow shifted the film in a very unique way," Redmayne said.
Jones said Hawking's response to the movie was all the more meaningful because he's not sentimental in the traditional sense of the word.
"It means a huge amount because he's someone who isn't phony in any way so when he shows genuine emotion, it is genuine," Jones said. "There are people who have great, great depths of feeling and emotion... in that quite English way, sometimes it's not always on the surface. But it's definitely churning away inside."
Jones said Hawking, his now ex-wife Jane Hawking (whose book, "Travelling to Infinity: My Life with Stephen," was the basis for the film), their children Lucy and Tim, and Jane's new husband will all attend the pic's London premiere.
Watch the trailer for The Theory of Everything Below: