Former Westpac executive George Frazis was forced out last Monday after leading the regional lender for three years, causing the bank's share price to drop 5.6 per cent.
Some large shareholders have called the bank's brief explanation for the sudden exit unsatisfying.
Chairman Patrick Allaway told the bank's annual general meeting on Tuesday that its board respects and acknowledges Frazis' contributions, but "reached a conclusion that we need a different capability and leadership style to build a simpler and more resilient bank".
"Our expectations, in respect of this, we made clear to George over a period of time," Mr Allaway said, according to text of his remarks posted to the ASX.
Having made that "difficult decision," Mr Allaway said, the board considered several options about how to move forward.
"We recognise the immediate departure of a CEO and the associated uncertainty is not ideal, but we felt a longer transition would not be in the best interest of BOQ," he said.
"We considered it would be sub-optimal and destabilising for George to continue in the CEO role knowing he did not have the ongoing support of the board while the search for his successor was underway," Mr Allaway continued.
Mr Allaway has stepped in as executive chairman while the bank looks to appoint a new CEO "as a matter of priority".
But the executive search and evaluation process may take up to nine months, he said.
Mr Frazis has yet to comment publicly on his ouster.
