Sixth-term councillor Bret Highsted has resigned from the Gore District Council.
In a letter to deputy mayor Keith Hovell, Highsted said since last year's election he had found the environment "highly stressful and the levels of anxiety unsustainable".
It was the latest controversy to arise since Ben Bell became New Zealand's youngest ever mayor at 23, when he ousted six-term incumbent Tracy Hicks by just eight votes at October's local elections.
Last week it was revealed Bell and the council's chief executive, Stephen Parry, were no longer on speaking terms.
Bell and Highsted had also shared a fraught relationship.
But Highsted was the highest polling candidate in his ward at last year's election and highly respected.
In his resignation letter, he apologised for commenting to an individual outside of the council before last week's behind-closed-doors extraordinary meeting.
Highsted stressed he had not disclosed any information following the meeting.
Parry said Highsted's contribution around the Council table would be missed.
"His peers and staff respected him for his agile mind and dedication to his role," he said.
In a statement from the council, no comment from Bell was included.
During last Tuesday's meeting, councillors unanimously agreed to appoint an elected member to function as an intermediary between Bell and Parry going forward.
Both men were given the opportunity to address the meeting and answer questions from councillors separately.
Bell was also removed from the committee which oversees the performance of the chief executive.
RNZ had obtained emails which showed things were prickly between the pair from early in the triennium.
It ultimately resulted in the entire executive sending a letter to the mayor outlining their concerns about his unwillingness to engage with staff, misrepresenting situations, a sense of staff being set up to fail, and putting the council and staff's reputations at risk.
A motion of no confidence in the mayor was also raised at last week's meeting by one of the councillors, before being dismissed by another as it would only be ceremonial as the mayor could not be removed by his council colleagues.
During the election campaign there were claims of dirty politics and the council had been beset by controversies this term.
Bell's initial choice as deputy mayor - Stewart MacDonell - was removed after a majority of councillors signed a letter calling for him to go.
That led to the appointment of Hovell with the unanimous support of council.
Bell had also faced controversy over his expenses, holding a retreat for elected members in Cromwell which was boycotted by some councillors, and his desire to hire an executive assistant.