Eddie added: "You can isolate the physicality or the voice, or ever the science, but making sure that they are not separate entities but embedded in one personality, that was the more complicated part."
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This awards season the two are finally gaining international recognition thanks to their incredible and powerful performances in The Theory Of Everything. Based on the early life of scientist Professor Stephen Hawking and his first wife Jane, Eddie and Felicity have both garnered SAG and Golden Globe nominations.
"It really does live with you for that time", said Felicity of playing a real person. "It did feel like one of those characters that I cared so much about her, and wanted to get all the complexity."
"It was wonderful to find this incredibly nuanced, complicated female character", added 31-year-old Felicity.
"When I met Jane she has this extraordinary ability to command the room and the strength and determination but also has great vulnerability and huge capacity for love and care and so it was a gift to play someone with all these nuances", Felicity added.
Eddie, who on Monday married his long term partner Hannah Bagshawe in a romantic winter ceremony, also discussed how the film was a learning experience for him, saying: "Everything about this film was an education, learning about the science because you need a base knowledge of what Stephen has achieved."
Professor Stephen Hawking also visited the set, and director James Marsh revealed how Stephen's visit raised the stakes for everyone, but especially for Eddie.
"When Eddie had to show us, out of sequence, four different versions of Stephen's disability and for that to work... was amazing."
The Theory Of Everything, in partnership with FindAnyFilm.com, show that great stories brought to the big screen are worth paying for, and is out in the UK on January 1st 2015.