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.
Derby owner David Clowes said: "I am thrilled that he shares our belief in the potential of Derby County and that he wants to play a leading role in our plans.
"When we bought the club, I was moved by the passion, solidarity and shared belief that bonded all of us who cared about Derby County. From the players, to the staff and to every single fan, we shared a determination to save the club and drive it forward.
"It's the same bond we need now as we get behind John and the players for these final 14 games. That bond was clear at Norwich last Saturday, a team fighting and refusing to be beaten, urged on by our magnificent support.
"This is now a season within a season and it's time for that passion, solidarity and shared belief again, to show what the Rams mean to us all."
Eustace, who has signed a contract which will run until the summer of 2028, 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.
He will be joined at Derby by assistant head coach Matt Gardiner and first-team coach Keith Downing.
As for Blackburn, who won 2-0 at promotion rivals West Brom on Wednesday night, interim boss David Lowe - who took charge of that game - is expected to remain at the helm for the home fixture against Plymouth on Saturday.
A statement from Blackburn, in announcing Eustace's departure, read: "While we are disappointed by [Eustace's] decision to leave at this crucial stage of the season, we fully understand that the opportunity to move closer to his family and return to a former club played a significant role in his choice.
"The club had hoped that John would see out the season and continue the fantastic work he has done, particularly after strengthening the squad in January and guiding us into a strong position in the league.
"However, with 14 games remaining and a real chance to push for a play-off place, the focus remains on achieving our ambitions.
"Football is always evolving, and while we part ways with John Eustace, this also presents an exciting opportunity for the new head coach to build on our current positive position.
"We remain in a good place in the league and the togetherness of the players, staff and supporters can all play a huge role in making it a successful end to the season."
Eustace 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."
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."
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
