Reading manager Paul Clement worked with Darren Bent at Derby County during the 2015/16 season.
The 46-year-old coach, who took charge of Reading earlier in 2018, was sacked by Derby in February 2016 after one win in seven.
Bent only scored one goal during Clement's eight month reign at Derby - and the unattached striker has laid into his former boss in a new interview.
"I know a lot of people were surprised when he got the sack at Derby," said the 34-year-old England international.
"But the players in the dressing room knew it was inevitable that he was going to crumble because training had changed, the intensity had changed, his philosophy that he'd brought in at the start of the season started going out of the window, because we weren't getting the right results and ultimately, he didn't really like confrontation.
"So when certain players who weren't in the team went to see him, they weren't really getting answers."
Pretty brutal stuff from Bent - that is until you see Clement's response on social media.
Clement responds on Twitter
The former PSG, Real Madrid and Bayern Munich assistant manager responded incredibly candidly to Bent's criticism.
Clement didn't hold back and his tweet is quickly going viral.
"I sense some bitterness here, which is normal if a player does not play much," tweeted Clement.
"It is never a difficult decision to leave out a player who is over weight and lazy."
It's rare to see a top-level manager behave this way on social media - but football fans on Twitter were absolutely loving it.
Clement's Reading side were beaten 2-1 by Derby County on the opening day of the 2018/19 Championship season.
"Clearly if you lose the game with the last kick it is tough," said Clement. "Particularly the first game of the season.
"We have just got to make sure we don't lose it. It was a fantastic cross and header."
Did Clement cross the line by calling Bent fat on Twitter? Let us know what you think by leaving a comment below.