Nitish Kumar said Tejashwi Yadav had no idea what he was talking about.
Bihar Chief Minister Nitish Kumar lost his cool at Tejashwi Yadav in the assembly on Friday after the opposition leader raised the criminal cases against him in a cutting attack days after the bitterly fought state elections.
"He's talking nonsense, he's lying," Mr Kumar fumed. "I keep listening because he is the son of a friend who's like a brother to me. I don't say anything. Who made his father leader of the legislative party does he know? Who made him Deputy Chief Minister? When there were allegations against him, I asked him to explain. He didn't so I had to leave," he said, referring to their 2017 split.
The Chief Minister's outburst came after Tejashwi Yadav, for the second time in a day, raised criminal cases against Mr Kumar in the assembly and also avenged an acerbic attack on his father Lalu Yadav during the election campaign.
Tejashwi Yadav called out a speech made by the Janata Dal (United) chief in which he had referred the Rashtriya Janata Dal supremo's large family, without mentioning them by name, and suggested it showed Lalu Yadav's preference of having male children.
"I hope the chief minister is aware that the youngest child of my parents was a girl, born after two sons," said Tejashwi Yadav, whose elder brother Tej Pratap Yadav is also a member of the state assembly and younger sister Rajlaxmi Yadav is married in the family of Samajwadi Party president Mulayam Singh Yadav.
"Now let us come to the fact that the chief minister has only one son. Could we apply his own yardsticks and say that he did not have another out of fear that it could be a girl?" Mr Yadav said.
The 32-year-old RJD leader, who was taking part in the debate on the governor's address to the newly constituted assembly, expressed dismay that while he focused on "people's issues" during the elections, the ruling National Democratic Alliance (NDA) resorted to personal attacks.
"I was speaking about jobs. And I bow before the people of Bihar who voted for us and helped us emerge as the single largest party. If not for manipulations by pliant officials posted in places where results of tightly contested elections were overturned, we might have got the chance to fulfil our promises," Mr Yadav alleged.
"But my opponents had other priorities. A person no less than the Prime Minister indulged in name-calling," said Mr Yadav, referring to the rallies of Prime Minister Narendra Modi where he used the expression "jungle raj ke yuvraaj" to target the RJD leader.
Last month, Nitish Kumar had taken no names in his taunt at the Yadav family about "having eight to nine children in the quest for a son" at an election rally.
Tejashwi Yadav, the eighth of former chief ministers Lalu Yadav and Rabri Devi's nine children, tweeted that even Nitish Kumar's insults were "blessings" for him. Later, he told reporters that the Chief Minister had insulted "women and my mother's sentiments".
Nitish Kumar was unusually caustic and, according to his critics, downright personal in his campaign against Tejashwi Yadav for the elections that brought him back to power earlier this month but cut down his party's seats dramatically.
Ties between Mr Kumar and Mr Yadav have been icy since the former ditched the RJD and Congress to go back to his old partner BJP two years after they swept the state elections in 2015. Both sides have frequently traded barbs since then but few recall the Chief Minister ever being this angry.