A previously unknown trove of more than 1,000 private letters of the last German Empress have been discovered in a hidden compartment at the Kaiser’s palace in Potsdam.

They include personal letters to Empress Augusta Victoria from her relative, Queen Victoria of England.

Augusta Victoria, Queen of Prussia and German Empress, was married to Wilhelm II, the Kaiser who led Germany into the disaster of the First World War.

The letters, which are still sealed in the envelopes Empress Augusta stored them in, could shed new light on the life of a woman who was witness to the upheaval of the early 20th century.

“We have found a treasure more precious than gems or jewelry,” Samuel Wittwer of the Prussian Palaces and Gardens Foundation said.

The grandson of Queen Victoria, “Kaiser Bill” was forced to abdicate after Germany was defeated in the First World War, bringing an end to the rule of House of Hohenzollern.

Empress Augusta followed him into exile and lived out the rest of her life in the Netherlands. But she appears to have left the letters behind in Germany.

They were discovered in a secret compartment at the Neues Palais in Potsdam, Germany’s answer to Versailles, where the Kaisers lived away in a world of parks and palaces.

Custodians stumbled upon the hidden compartment when they were trying to unlock a vault that had also lain undetected for decades.

“There are many nooks and crannies in the palace you don’t pass by every day,” Mr Wittwer explained to Deutschlandfunk radio.

“I’ve been here with the Foundation for 19 years now. I’m a very curious person, I have a key that fits everywhere, and I have to say that I saw this vault for the first time at the end of last year. Of course we immediately thought of gems and jewelry and pearls and what we still need to finance the exhibition, and we wanted to open the vault.”

Potsdam lay in communist East Germany during the Cold War, and it is unclear why the vault and hidden compartment were undisturbed for so long. Soviet troops ransacked the palace in 1945 and took most valuables away, but appear not to have broken into them.

The vault, it seems, is exceptionally secure. Four different security companies tried and failed to open it. Eventually the foundation resorted to inserting an endoscopic camera, which revealed that the vault was empty.

But in the process they discovered a secret door next to the vault made of wood, which were they were able to open. Inside they found the letters. 

“Of course that was an insane sensation. They came right in and found the trove: two wooden boxes full of envelopes, and a whole bundle of letters in each envelope,” Mr Wittwer said.

“She did not want anyone to read these, it’s her private letters in those boxes, from when exactly we do not know.”

The newly discovered letters have yet to be read. For the time being they are being displayed still sealed in the envelopes in which they were found as part of a special exhibition on the twilight of the Kaisers.

When the exhibition ends in November they will be opened on the 100th anniversary of Wilhelm’s abdication.

“It feels a little sacrilegeous to open such an envelope just like that, when it was sealed 130 years ago and no one even knew where it was, for 100 years,” Mr Wittwer said.

The letters from Queen Victoria could shed light on relations between the relatives in the run-up to the First World War.

But historians do not hope to find any of the Kaiser’s letters to his wife: according to contemporary accounts she burned all of those before leaving Potsdam for the last time and heading into exile.