A massive, two-volume edition of Adolf Hitler's notorious Nazi manifesto has become a non-fiction best-seller in Germany one year after it was published, the publisher announced on Tuesday.

The edition called "Hitler, Mein Kampf: A Critical Edition" has sold 85,000 copies, shocking the book's publisher. The Munich-based Institute for Contemporary History (IfZ) said a sixth print run will go on sale later this month.

"These sales figures have taken us by storm," Andreas Wirsching, who heads the IfZ, told German news agency DPA.

"No-one could really have expected them," Wirsching said.

IfZ spent years adding comments to Hitler's original text to highlight the dictator's propaganda. The resulting edition is 1,948 pages long, has a plain gray cover, contains around 3,700 footnotes and costs a hefty 59 euros ($62).

The institute planned an initial print run of up to 4,000 copies and was uncertain if more would be printed. By April of 2016, the book topped the German weekly "Der Spiegel's" non-fiction best-seller list.

It was the first version to be published in Germany since the end of World War II when the copyright held by the Bavarian state government expired at the end of 2015.

Book-buyers not 'radical'

Reacting to concerns that the book could promote far-right ideologies, the institute organized a series of presentations and debates across Germany and in other European cities to gauge the impact of the new edition.

"It turned out that the fear the publication would promote Hitler's ideology or even make it socially acceptable and give neo-Nazis a new propaganda platform was totally unfounded," Wirsching said in a statement.

IfZ also reviewed data collected by regional bookstores about the book's buyers. The data showed that the book's buyers tended to be "customers interested in politics and history as well as educators" and not "reactionaries or right-wing radicals," the institute said.

Hitler wrote his Nazi manifesto in two volumes in the mid-1920s after he was thrown in prison after his failed Munich putsch in 1923.

The book, which translates to "My Struggle," outlined Hitler's crude anti-Semitism and called called for Germans to be granted "Lebensraum" or living space. The ideologies helped lay the basis for Nazi military aggression in Eastern Europe and the Holocaust

For over 70 years, Germany refused to allow the anti-Semitic book to be republished out of respect for victims of the Nazis and to prevent inciting hatred.

A far-right publisher announced last year that it planned to print an edition without any annotations, prompting an investigation of suspected incitement of hatred. Prosecutors later said there was no indication the book went on sale.

rs/rc  (AP, AFP, dpa)