A German prince was arrested, along with other alleged plotters, in a massive operation by German security forces Wednesday
A German prince was arrested, along with other alleged plotters, in a massive operation by German security forces Wednesday AFP

A German prince, known for his desire to revive the country's monarchy and rejected by his own family as a "mad old man", has emerged as a central figure in an alleged coup plot.

Prince Heinrich XIII Reuss, descendant of a noble family with a history dating back over eight centuries, was supposed to be installed as Germany's new leader if the bizarre plan had succeeded, officials say.

But he was arrested, along with other alleged plotters including a right-wing ex-MP and former soldiers, in a massive nationwide operation by thousands of German security forces Wednesday.

The group are alleged members of the "Citizens of the Reich" ("Reichsbuerger"), an ideological movement grouping far-right extremists and conspiracy enthusiasts.

The suspected seditionists are said to have planned to storm parliament and had sketched out details of their new government.

Heinrich XIII, a real estate businessman, was arrested at his residence in Frankfurt and led out by police wearing masks.

At the same time, his castle in Bad Lobenstein in the eastern region of Thuringia -- where his aristocratic family had once ruled over a swathe of land -- was also searched.

It was at this grand residence where the prince allegedly plotted with others to overthrow the government.

The 71-year-old had made little attempt to hide his extreme views, which chimed with the "Reichsbuerger" movement's belief in the continued existence of the pre-World War I German Reich, or empire, under a monarchy.

In a rambling speech to a conference in Zurich in 2019, he lamented the abdication of the German emperor in 1918, and insisted the modern-day German republic was illegitimate.

He referred to the "so-called Federal Republic of Germany" and said the country was "being controlled based on administrative structures installed by the Allies after World War II", who had also written the constitution.

Other descendants of the noble family have starkly different views however, and have long been trying to distance themselves from him.

The prince is "unfortunately a mad old man," the family's current head, Prince Heinrich XIV Reuss, told AFP, adding they had cut ties with him 14 years earlier.

"There is no contact with this black sheep of the family."

The head of the house, who is based in Austria, said he was "very shocked" to hear of his relative's alleged involvement in the plan to overthrow the government.

"It is very bad for the family's reputation, no question," he added.

On Thursday, federal police chief Holger Muench said the far-right group behind the plan was heavily armed and posed a real threat.

Those arrested included "a dangerous mix of people with irrational convictions, some with a lot of money and others in possession of weapons", he told the ARD broadcaster.

Weapons including crossbows, rifles and ammunitions were uncovered during Wednesday's raids, he said. Twenty-five were arrested in the raids while more are under investigation for their links to the group.

Still, views differed as to how serious the plot really was.

A comment piece in the Sueddeutsche Zeitung daily warned it would be naive to dismiss the group as "loonies".

It noted the plotters included "teachers, doctors, business people... They are people who should actually be pillars of democracy".

The Frankfurter Allgemeine Zeitung daily, however, cautioned against "getting too carried away", as nothing suggested the plot would have succeeded.