Fritz von Weizsäcker, who worked as a doctor, had just delivered a lecture on liver diseases at the Schlosspark hospital in the western Berlin neighbourhood of Charlottenburg on Tuesday evening when he was stabbed, a police spokesman said. One other person was seriously injured.

The 59-year-old, a father-of-four, died at the scene despite efforts to save him. The incident took place around 6.50pm.

Around 20 people were in attendance at the lecture. The suspect was overpowered by the other people present, one of whom, said to be an off-duty policeman, was severely injured by the attacker.

Prosecutors said the 57-year-old attacker had bought the knife in his home state of Rhineland-Palatinate in the far west of Germany and travelled to Berlin by train.

They said he had been diagnosed with an “acute mental illness” and had a “probably delusional general dislike” of the Weizsäcker family.

Police tweeted about the “violent attack” on Tuesday night.

Head of the pro-business FDP party, Christian Lindner, paid tribute to his friend on Twitter, calling him a “passionate doctor and a fine person”. He voiced his grief, saying that “once again we ask ourselves what sort of world are we living in.”

His father, Richard von Weizsäcker, was considered one of Germany's great post-war political figures.

Spiegel magazine said the suspect had researched the elder Weizsäcker's role on the board of chemicals giant Böhringer Ingelheim during the 1960s before he began his political career.

The company at the time reportedly supplied the United States with some of the chemicals in Agent Orange, a powerful defoliant used in the Vietnam War that caused severe health problems for humans exposed to it.

Weizsäcker was president of West Germany from 1984 to 1990, and then held the same position in the united Germany from 1990 to 1994.

He was previously a deputy in the lower house of parliament for the CDU now led by Chancellor Angela Merkel, and mayor of West Berlin. He died in 2015.

Merkel said the killing was “a terrible moment for the von Weizsäcker family”, her spokesman Steffen Seibert told reporters.