Two former Israeli prime ministers have faced off in court in Tel Aviv, as Benjamin Netanyahu and his family began a defamation suit against Ehud Olmert.
Mr Netanyahu, his wife Sara, and their eldest son Yair are suing Mr Olmert for $269,000 (£198,000) in damages for saying that they were mentally ill.
Mr Olmert made the claim in two Israeli TV interviews last April.
He is arguing that it was not libellous because it was true, and also that he was clearly expressing an opinion.
The suit filed by the Netanyahus accuses Mr Olmert of "obsessive efforts to harm their good name in public, out of jealousy and deep frustration".
It is based on two interviews he gave in the wake of Israel's last general election, when Mr Netanyahu was attempting to remain in power while standing trial on corruption charges.
In the first, Mr Olmert told DemocraTV: "What can't be fixed is the mental illness of the prime minister and his wife and son. That's not fixable."
In the second interview, with Channel 12, he refused to retract the claim and laughed when warned that he might be sued.
At Monday's hearing Mr Olmert was asked by Judge Amit Yariv what he had based his comments on.
"I followed their actions, I heard recordings of the family, I conferred with experts and people who are associated with them and know them well," he answered, according to the Times of Israel. "They described to me behaviours that are popularly seen as abnormal, crazy behaviour."
The Netanyahus' lawyer, Yossi Cohen, said: "A family is sitting here that in my eyes is one of Israel's finest, and they have to hear that a former prime minister - who by the way does not have a clean past - calls them mentally ill?"
He added that "in a different country Olmert would have been arrested", to which the judge responded: "Thank God we don't live in that country."
Judge Yariv suggested that Mr Olmert should "state for the record that his comments were an opinion, and that he does not know whether they are truth or not truth". If he continued to argue that they were true, the judge warned, he would require a higher burden of proof.
In remarks directed at both sides, the judge said it was "unfortunate that a painful subject such as mental illness is being taken and turned into a circus". The hearing was adjourned and will resume at a later date.
Mr Olmert was the first former Israeli prime minister to be imprisoned.
He resigned as the leader of his party in 2008 after being placed under investigation for corruption, but remained prime minister until elections the following year that brought Mr Netanyahu to power.
Mr Olmert was eventually convicted of bribery, fraud, breach of trust and obstructing in a series of trials in 2014, but only began serving a 27-month prison sentence two years later.
Mr Netanyahu lost his 12-year hold on power in June last year, after opposition parties united to unseat him and formed a government led by Naftali Bennett.
He had refused to step down while standing trial on charges of bribery, fraud and breach of trust. He denies any wrongdoing.