Prince Heinrich XIII Reuss is among a nine-strong group on trial in Frankfurt in one of the biggest cases heard by German courts in decades.

Prosecutors accuse the group, which includes a former politician and ex-army officers, of preparing a “treasonous undertaking” to storm the Bundestag and take MPs hostage.

Reuss, a minor aristocrat and businessman, is one of the alleged ringleaders and was in line to become the provisional head of state after the government was overthrown, according to prosecutors.

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But the 72-year-old told the Higher Regional Court in Frankfurt: “I cannot confirm what I am accused of in substance.”

He then gave a lengthy account of his life, which he said was marked by “traumatic” events.

“It is important to understand me as a person,” said Reuss, who is in custody, adding that he was in an “unstable” state.

He described a troubled childhood, during which he was physically and psychologically abused at school by his teachers.

Health problems resulting from a car accident led to him being discharged from the army. His Catholic parents rejected his marriage to an Iranian woman, now his ex-wife, he said.

“Even if she had been the daughter of the emperor of China, they wouldn’t have accepted her,” Reuss said.

Defence lawyer Roman von Alvensleben said he aimed to prove Reuss was not “a man who wanted to provoke violence, that he does not want to kill people, that he is not a danger to the Republic of Germany”.

The sensational plan, announced by authorities at the end of 2022, is the most high-profile example of what is considered a growing threat of fringe violence in Germany. The biggest threat is from the far right, according to officials.

The alleged plotters are said to have taken inspiration from conspiracy theories, including the global QAnon movement, and drawn up “lists of enemies”.

They belonged to the German Reichsbuerger (Citizens of the Reich), a political movement of extremists and gun enthusiasts who reject the legitimacy of the modern German republic.

The proceedings, in which a total of 26 people face trial, are being held across three different courts — Frankfurt, Stuttgart and Munich.