David Seidler, who penned the script for the BAFTA-nominated picture, told the New York Post that the film's eventual lead Colin Firth was not his first choice for the part.
However, Seidler admitted that he soon realised Firth was the "perfect" actor to play the stammering monarch.
"When I initially wrote the screenplay, I immediately had Geoffrey Rush in mind for [speech therapist] Lionel Logue," Seidler said. "But I thought Paul Bettany would be the actor to play the king.
"I wanted Paul, but I was lucky that it was decided the role would go to Colin. As soon as he read for it, I knew he was perfect."
Firth recently picked up a Golden Globe and a BAFTA nomination for his performance in the film.