John Eustace has left Blackburn Rovers to become the new head coach at their Championship rivals Derby County.
Rovers are fifth in the Championship table and well and truly in the play-off hunt - but Eustace has departed for a club sitting just outside the second-tier's relegation zone, separated only by goals difference.
Eustace ended his playing career with Derby in 2015 - and his first game in charge is set to be a trip to QPR on Valentine's Day, live on Sky Sports Football.
Blackburn said on Sunday they were "extremely disappointed" with Eustace after he "requested permission" to speak with Derby, who had activated a clause in his contract, "at such a crucial stage of the season".
He took charge at Blackburn 12 months ago, soon after being controversially sacked by Birmingham. The Lancashire club were 18th in the Championship at the time, but now lie in the top six.
Speaking last Sunday, Eustace said he wanted to talk to the Rovers ownership and, asked if he would be seeking assurances that he would continue to be well supported by the club, he said: "Of course."
Was Eustace mis-sold the Blackburn project?
Sky Sports' Don Goodman:
"We're not behind the scenes so it's the old adage: you don't know what's going on behind closed doors. You can only assume that there were relationships with the hierarchy or reassurances of what the future holds that Eustace didn't particularly like.
"He did a brilliant job at Blackburn, he went in last February when they were in a bit of bother. He got them out and I don't think anybody would have expected Blackburn to be where they are now.
"He brought some players in but they have mainly been free transfers or loan deals. So you wonder what the relationship with the hierarchy was behind the scenes. You can only assume that he was slightly mis-sold the project when he signed on the dotted line a year ago.
"The only logic is if Eustace gets more excited about the project at Derby County than he can get in the immediate future at Blackburn, then it's the only thing you have to go on.
"When you look at the money they have brought in over the few years: Ben Brereton Diaz, Adam Wharton and Sammie Szmodics. The money has come into the football club and they certainly haven't outlaid much of that in real terms.
"So I just wonder what reassurances John had. He was trying to build a team that is able to get Blackburn competing at the top of the Championship and with a bit of luck, up to the Premier League."
Eustace's first six fixtures at Derby - including Blackburn at home!
February 14: QPR (A), 8pm kick-off, live on Sky Sports Football
February 22: Millwall (H), 12.30pm
March 1: Middlesbrough (A), 3pm
March 8: Blackburn (H), 3pm
March 11: Coventry (H), 7.45pm
March 15: Plymouth (A), 3pm