What may be the only existing copy of Emperor Hirohito’s account of World War II and the era leading up to the conflict is set to go on the auction block in New York next month.

The 173-page, two-volume document — known in Japan as “Showa Tenno Dokuhakuroku”(“Emperor Showa’s Monologue”) — was dictated by the Emperor to several of his aides soon after the war and transcribed word-for-word by senior diplomat Hidenari Terasaki. It was published by the monthly Bungei Shunju magazine in 1990, causing a national sensation.

Emperor Hirohito is posthumously known as Emperor Showa.

London-based auction house Bonhams said on its website that the volumes will be auctioned in New York on Dec. 6, with the document expected to fetch an estimated $100,000 to $150,000.

“Bonhams is thrilled to have been given this opportunity to sell the only extant copy of a document that is critical to our understanding of 20th-century world history,” Joe Earle, Bonhams Senior Consultant for Japanese Art, said in a statement.

The Emperor’s recollection of the turbulent time period was recorded in preparation for the postwar International Military Tribunal for the Far East, better known as the Tokyo Trial, historians say. In 1946, five aides recorded the Emperor’s account from March 18 through April 8. The tribunal started in May the same year.

Parts of the memoir were translated into English and submitted to the postwar Allied Occupation forces.

The Emperor discussed topics such as Japanese politics at the time, Japan’s assassination of Manchuria warlord Zhang Zuolin in 1928 and the nation’s surrender at the end World War II in August 1945.

The Emperor’s frank discussion about the history of the war has caused heated debate among historians, including how much the leader himself was responsible for key political decisions during Japan’s wars and conflicts in the 1930s and 1940s.

“His aides tried to prove the Emperor was a peace-loving leader to prepare for the Tokyo Trial. That was their biggest motivation,” historian Ikuhiko Hata told The Japan Times on Tuesday. “So you have to carefully read the text, but the account is very interesting.”

Bonhams didn’t say who currently owns the document.

The document was originally discovered in Terasaki’s belongings held by his daughter, Mariko Terasaki Miller. Her mother, Gwen Harold Terasaki, born in Johnson City, Tennessee, was the author of a best-selling war memoir “Bridge to the Sun,” which was also made into a move and detailed her family’s experiences during the war.

According to Hata, historical records suggest at least another two aides to the Emperor separately transcribed his accounts of history on different occasions. The government should disclose those records if they still exist, Hata said.