As a child visiting his grandfather's grave, Prince Friedrich Solms-Baruth V was given his life's mission.

Key points: Prince Friedrich Solms-Baruth V is suing Germany for his family lands back

Prince Friedrich Solms-Baruth V is suing Germany for his family lands back The estate was confiscated by the Nazis after his grandfather helped plot to kill Hitler

The estate was confiscated by the Nazis after his grandfather helped plot to kill Hitler Previous court cases have ruled that Prince Friedrich III willingly signed away his estate

"I was taught that if Germany was ever to reunify … then this would be my job: to make sure that the Nazis wouldn't get away with their evil trick that they played on my grandfather," he said.

For more than a decade, he has been trying to recover what he believes to be his family's rightful property, which he said was stolen by Nazis 75 years ago.

His mission has also been to prove that his grandfather was the victim of a cruel strategy led by the head of the Gestapo, Heinrich Himmler, to hide the seizure of land.

"I simply want to uncover the truth and let the facts speak for themselves [to reveal] what the Nazis tried so hard to cover up, by cloaking their crimes in a veneer of legality all these years," he said.

Prince Friedrich at his grandfather's grave, where he vowed to win back his family's estate. ( Supplied: Friedrich Solms-Baruth V )

"We're essentially a one-man show against the entire federal government."

He now believes he has the proof to make his a "landmark case" which highlights the "fiendish" methods used by the Nazis to take possession of property.

"We have now found incontrovertible evidence to uncover the truth. There was a major cover-up by the Nazis of what they knew themselves was an illegal action," he said.

'He absolutely abhorred Hitler'

By 1944, Prince Friedrich's grandfather — his namesake, Prince Friedrich Solms-Baruth III — had become an outspoken critic of Hitler, and had been aiding a plot to kill him.

Prince Friedrich Solms-Baruth III was part of the 1944 plot to assassinate Hitler in Wolf's Lair. ( Supplied: Prince Friedrich Solms-Baruth V )

"He absolutely abhorred Hitler long before he came into power, and predicted that he would ruin Germany," his grandson said.

"He called him a 'madman' and a 'cretin' and refused to have anything to do with him."

Prince Friedrich III had loaned his homes to a group of German military officers who were planning Operation Valkyrie, the infamous plot to kill Hitler at his Wolf's Lair headquarters in East Prussia.

When the assassination attempt failed on 20 July 1944, Prince Friedrich was one of thousands arrested by the Gestapo.

In exchange for his life, his grandson said Prince Friedrich III was tortured and coerced into signing away his estate.

A bomb was planted in a suitcase in a conference room, but Hitler survived the blast. ( Wikimedia Commons: German Federal Archives )

As a member of a prominent aristocratic family stretching back to the 16th century, the prince's estate encompassed manor homes, villages and agricultural land in Germany and Poland.

Most of the property in Germany now officially belongs to the state of Brandenburg, the town of Baruth and other towns in the region.

"We have always said we would never touch any private individuals who bought [property] in good faith," Prince Friedrich V said.

"We're only interested in obtaining the land that was stolen by the Nazis and is still being kept by the federal government."

In 2003, the family was awarded a portion of land by the federal German government.

Prince Friedrich has bought back some of his family's seized homes and is now focusing his legal fight on their land. ( Supplied: Prince Friedrich Solms-Baruth V )

But Prince Friedrich V has been unable to convince German authorities that his family should have the remaining forestry estate handed back.

Courts have ruled that he cannot prove that his grandfather was coerced into giving away his land.

"They said [my grandfather] negotiated with the Gestapo and had been able to achieve positive terms for himself, and had therefore received preferential treatment. I was shocked," he said.

The Federal Administration Court told the ABC it cannot comment on ongoing cases.

Ink in secret documents could prove monumental

For years, Prince Friedrich has been trying to prove the Solms-Baruth estate was "stolen" as part of a plan by Heinrich Himmler to loot Germany's wealth for the Gestapo.

The prince signed over his estate to Gestapo head Heinrich Himmler (left). ( Reuters via The National Archive )

In 2017, a researcher working on the Solms-Baruth case made a "fluke" discovery.

The documents were found by chance in online government archives.

Prince Friedrich insists this is "incontrovertible" evidence showing his grandfather did not freely cut a deal with the Nazis to hand over his properties.

"It was top-secret. In this Himmler decree, it states point-for-point, how to take properties from enemies of the state, without confiscating it officially in the deeds book," Prince Friedrich said.

"If you compare the decree and the methods that were deployed against my grandfather, they just went down the list and did it exactly according to this Himmler decree."

Prince Friedrich says this document is a secret order instructing the SS on how to handle confiscated properties. ( Supplied: Brandenburger Landeshauptarchiv )

Prince Friedrich says Heinrich Himmler believed he could unseat Hitler by hoarding money.

"Being very intelligent and devious as he was, he aimed to achieve complete economic and financial independence for the Gestapo and SS in order to achieve this aim."

Another discovery made by Prince Friedrich's researchers could have major implications for other German families who lost their estates.

At the Brandenburg State archives, experts set out to prove the instructions to destroy the Solms-Baruth title deeds were drawn up before the Nazis surrendered in May 1945.

They found that the ink on the documents contained amounts of iron. In documents drawn up after the fall of the Nazi regime, the iron is missing.

Prince Friedrich sees this as the smoking gun for many German families.

"This affects families who may have been told that their properties were confiscated after May 1945," he said.

German landowners who were told their properties were seized by Soviet occupiers following World War II cannot win back their estates.

In 2005, the European Court of Human Rights ruled that Germany could not be held responsible for the actions of Soviet occupiers.

If the court ruled in favour of the families, the German government would have had to pay billions of dollars in restitutions.

"Now we realise that we are in the same boat of hundreds if not thousands of families … which is what makes it such a landmark case," Prince Friedrich said.

'This was my life's duty'

The discovery of what he considers to be compelling new evidence has been a driver for Prince Friedrich to continue his fight, which he describes as a "taxing and stressful journey."

"The case has now taken on a much larger dimension for myself and a much larger moral significance than just my grandfather's case alone," he said.

During World War II, the Nazis' seizure of property and possessions from families and organisations it was persecuting was immense.

In 2017, the Institute for Jewish Policy Research said the German Ministry of Finance reported it had paid more than $3 billion in compensation for lost property in the former East Germany since the end of the war.

It was not until the unification of Germany in 1990 that property restitution in East Germany took place.

The Conference on Jewish Material Claims Against Germany says the vast majority of claims have since been decided in administrative and court proceedings.

The Solms-Baruth case has stretched 20 years; it's now reached the Federal Constitutional Court and the Federal Administrative Court in Germany.

If Prince Friedrich V fails there, he would like to have the case heard at the European Court of Human Rights.

The Prince escaped execution but was imprisoned for nine months after the assassination attempt. ( Supplied: Friedrich Solms-Baruth III )

After being released, Prince Friedrich III fled Germany and took refuge with some of his relations in the Swedish royal family, before taking his family to Namibia, where he died in 1951.

His grandson believes he owes to his grandfather — and thousands of others — to try to reclaim what was lost.

"I have a feeling that this is just a general strategy to deal with restitution claims. I'm just one of so many," he said.

"The general strategy is to hope … that eye-witnesses die out, claimants will run out of finances, [or] they'll run out of steam.

"So many people in my position have done exactly that, but in my case I was told from when I was very small, that this was my life's duty," he said.

If the land is ever restituted, Prince Friedrich’s vision is to use it to create job opportunities for young men and women.

"To do something environmentally friendly — perhaps based on alternative energy — there is more than sufficient land to do that on a large scale and create jobs at the same time."