Garry Monk has revealed he is no longer on speaking terms with former assistant Pep Clotet, suggesting a lack of trust led to a breakdown in their relationship.
Sheffield Wednesday manager Monk's spicy remarks come ahead of his side's Sky Bet Championship clash with Clotet's Birmingham at Hillsborough on Wednesday night.
Clotet had previously worked with Monk at Swansea and Leeds before the duo teamed up again at Birmingham in March 2018.
The Spaniard then took charge at St Andrews over the summer after Monk was sacked in June.
Although Monk stopped short of claiming he was knifed in the back by Clotet, at his pre-match press conference he said: "In terms of the, I don't know what it is... is it interim, caretaker, head coach? I'm not sure what his title is, but I don't speak with him.
"I think what's most important to me is when I'm assembling a staff around me to work with me, the key for me is to give them opportunity.
"It is to show them that complete trust and you hope that they repay that trust with hard work and loyalty.
"Sadly, not everyone has those values in their character. Some choose to pursue their own opportunities in the worst possible way."
Monk added: "I think the most important thing for me is that you live and you learn.
"Unfortunately for me, I didn't listen to a lot of people in football circles who warned me about the type of character he is.
"But, yeah, that's an error in judgement from myself. It's a mistake that I won't be making again in the future."
City hit back via their Twitter feed, pointing an accusing finger at Monk for lacking class, and posting the video of his remarks on Clotet.
The tweet read: "We tried to find comments from our 'Interim Caretaker Head Coach' speaking without class about tomorrow's game. We couldn't.
"In the meantime, it's always nice to hear something from the opposition manager. Garry, you want to come?!"
The two sides go into the game out of form, with the Owls picking up just two points from their last four matches, while City have taken one point from their last three.
Monk is without full-back Liam Palmer, who starts a three-match ban following his red card late in the 2-1 defeat at West Brom on Saturday, while Cameron Dawson replaces Kieren Westwood in goal as the latter has a minor shoulder injury.
Birmingham captain Harlee Dean completes a three-match ban.