A notebook said to contain detailed mathematics and computer science notes written by Alan Turing, the British cryptographer, is going up for auction in April. Turing cracked the Nazi enigma code at the height of World War II, helping push the Allies to victory. He's also the subject of the Oscar-nominated film, “The Imitation Game” starring Benedict Cumberbatch.

The notebook, dated to 1942, has never been seen in public but is expected to demand as much as $1.5 million when it goes on sale at Bonhams auction house in New York April 13. The notebook could contain previously inaccessible information about the birth of computer science and artificial intelligence, which Turing labored over for decades before his death in 1954.

“The contents of the journal are intensely personal, so it is not a surprise that he would want to keep the journal private, and in fact, it remained hidden amongst his personal effects until his death,” a Bonhams press release stated in announcing the sale. “As he wrote at the beginning of this journal, 'It seems a suitable disguise to write in between these notes of Alan's on notation, but possibly a little sinister; a dead father figure, some of whose thoughts I most completely inherited.'”

Turing didn't receive credit for deciphering Nazi communications until decades after his death. He committed suicide in 1954 after receiving chemical hormone treatment that sought to cure his homosexuality, which was illegal in Britain at the time.

Before his death, Turing gave the notebooks to a friend, who kept them hidden. 

His story is the focus of “The Imitation Game,” which has been nominated for Best Picture at the 2015 Academy Awards. It has also inspired notable Britons to call on the government to pardon more of the thousands of people arrested for homosexuality during the era when Turing lived.