Steve Bruce has thanked Hull City fans for their "unwavering" support and says he resigned as manager on Friday "for the sake of the club".
Bruce joined the Tigers in 2012 and led them to promotion to the Premier League twice and also an FA Cup final.
His resignation followed a breakdown in his relationship with vice-chairman Ehab Allam.
"It was a decision I had to make for the sake of the club," he said in an open letter to the Hull Daily Mail.
"The last 12 months have been very tough and it felt like the right step for the club to move forward in a different direction and with someone else in charge."
Hull's owners put plans to sell the club on hold on Wednesday to "ensure stability in the transfer window", with the senior squad reduced to only 13 fit players.
Bruce continued: "It is rare for a manager to have the backing I've had from fans. It's been unwavering.
"One of the abiding memories was the reaction of supporters the day we were relegated on the final day of the 2014-15 season.
"They applauded us off the pitch when you'd expect them to have been ripping the roof off."
Diame's 'sadness' at departure
At an event to reveal a new "club-record" sponsorship deal, Hull midfielder Mohamed Diame admitted he was "really surprised" by Bruce's decision to leave.
"As everyone knows he was an important man for us here and everybody's sad, but life continues," he told BBC World Service.
"I knew it was going to be a tough pre-season because we had a lot of injuries and we didn't see any new players come in, but I wasn't expecting him to leave.
"The most important thing is now is to get players, to be honest. We have got too many injuries and the squad is not big enough so we need players.
"We need to bring some players to support us to get a bit of stability because at the moment we are not stable."