Lionel's grandson Mark Logue was consulted for the script of the movie, starring Colin Firth as the stammering King George VI and Geoffrey Rush as his elocution coach, widely tipped for Oscar glory at the Academy Awards next month.
His involvement encouraged him to return to hundreds of documents about his grandfather's inspiring story, resulting in the book "The King's Speech: How One Man Saved the British Monarchy" which he wrote with journalist Peter Conradi.
At his home in London, Mark Logue sifted through piles of letters, including several from the king to Lionel which reveal a surprising level of intimacy between the king and, to use Lionel's own words, a "common colonial."
An appointment card covered with Lionel's tiny writing shows how the future king visited his Harley Street practice 82 times between October 1926 and December 1927, and describes the royal's "very flabby" waist as well as his speech impediment.
A scrapbook of press cuttings, photographs of Lionel and his wife Myrtle at King George VI's coronation, Christmas cards from the royal family and Lionel's own diary attest to his pride at having helped the monarch through his tumultuous reign.
But Lionel also had a sense of being someone from another country and another class.
"Here we've got a man in his mid-40s, emigrating from Australia with his young family and setting up in the heart of the British medical establishment in Harley Street, very much an outsider," Mark Logue said in an interview.
"Within two years he's treating the king's son. Then he's kind of catapulted into the center of the royal family when he (the Duke of York) becomes king.
"All the time I think he's had this sense that he's an outsider, but also proud of it. He says in his diaries, frequently, that the king sought his advice ... as a commoner -- what does a common man on the street think," he added.
