Secret notebook of Imitation Game codebreaker Alan Turing to be auctioned

When the codebreaking genius Alan Turing died, he left much of his life's work to Robin Gandy, another mathematician and close friend.

Most of those papers now reside at the archives in King's College in Cambridge, England. But Gandy kept something special for himself: A notebook of Turing's handwritten thoughts, from the wartime period during which he was trying to break the famed Enigma Code.

That notebook is now coming up for auction and Bonhams expects it to fetch more than US$1 million.

The auction - scheduled for April 13 in New York - comes months after the release of The Imitation Game, an Oscar-nominated a biopic of Turing. Turing was gay, a criminal offence in England at the time, and he was forced to undergo hormonal therapy to "cure" him after a 1952 conviction. He committed suicide two years later.

Bonham's press release announcing the auction plays up the Imitation Game tie-in and even contains a quote from star Benedict Cumberbatch about how "the thought of being able to hold a manuscript that was written by him is thrilling".

Cumberbatch received a best actor Oscar nomination for his portrayal of Turing, one of eight nominations for movie, including best picture.