When The King’s Speech racked up 12 Oscar noms on Tuesday, the acting talents of Colin Firth, Geoffrey Rush and Helena Bonham Carter were widely lauded. But it is the crux of the real-life relationship between King George VI of England and speech therapist Lionel Logue, that provides the actors with the basis for their compelling performances. Lionel’s grandson, Mark, inherited his grandfather’s archive of the work he did with the British monarch and the friendship they developed, and worked with author Peter Conradi to write The King’s Speech: How One Man Saved the British Monarchy a companion book to the movie. What is not shown in the film is the longevity of the friendship between these two men, which began when Australian-born elocution instructor Lionel started work with the Royal to overcome his stutter. The two remained friends for the rest of their lives, and the collection of hundreds of letters between Lionel, George VI and his wife Elizabeth chronicle a long term bond. “The content of the letters between them is incredibly friendly as you’d expect between two friends,” Mark Logue tells CNN.com. “But there is a kind of etiquette that Lionel still abides by,” always opening letters with “your Royal Highness.”

After World War II, when Lionel’s wife Myrtle passed away unexpectedly, the King sent him a heartfelt note: “Dear Logue, I must send you one line to tell you how terribly sorry I was to hear of your bereavement. And I send you all my deepest sympathy in your great grief …I do so feel for you as I know you had a perfect companionship with her. I am yours sincerely. George.”

Grandson Mark is deeply touched by these sentiments, though he was born years after the two friends had passed. “It’s something about thinking about him hurting after Myrtle’s death… makes it kind of real,” he explains.

Along with the letters, the archive contains notes, scrapbooks and what Mark believes to be an annotated copy of the speech George VI delivered over the radio in 1939 as Britain entered the war with Germany, the speech central to climax of the film. Tom Hooper, director of The King’s Speech, consulted the archive a few weeks before filming began, and discovered a few unknown details that were then added to the movie. An entry from Lionel’s diary prompted a joke to be included.

“I went to Windsor on Sunday for the broadcast… only one mistake… W in weapons,” Logue recorded. “After the broadcast I shook hands with the King and congratulated him. And asked him why he stopped on the W. He replied with a grin. I did it on purpose. I exclaimed — on purpose ? And he said yes — if I don’t make a mistake they won’t know it’s me.”