A unique document relating to the capitulation of Rotterdam during World War II has been found at a German auction house, news agency ANP says on Thursday.

The hand-written document details the second ultimatum made by the German occupiers ahead of the bombardment of Rotterdam, which led to the city’s surrender.

The bombardment took place on May 14 as the Dutch negotiator was heading back to his chiefs with information about the second ultimatum. It destroyed almost the entire city centre, killing nearly 900 people and making 85,000 others homeless.

The papers were found by researcher Gerard Groeneveld and are included his new book about Rotterdam’s role during the war.

Groeneveld says the document was last seen by the city’s mayor P J Oud while the terms of the surrender were being finalised. He told a parliamentary inquiry after the war it had vanished in the chaos.

The document had been offered for sale in the online auction by a French collector, broadcaster Nos says.