Coach John Kear is to leave Hull FC with immediate effect after the club announced it would not renew his contract at the end of the season.
Kear guided Hull to victory in the Challenge Cup last season
Following "amicable discussions" on Monday, the club also confirmed that Kear's contract will be honoured.
Kear said: "It has been a tremendous period of my working life and I wish all at the club the best of luck for the future."
Kear's assistant, Richard Agar, is a likely stop-gap appointment.
Steve McNamara, currently assistant coach at Bradford, could take the permanent post.
In a statement, chief executive David Plummer said: "Hull FC wish to place on record their appreciation for John's efforts over the past three and a half year and wish him all the best for the future."
The announcement ends speculation over Kear's future since the club failed to discuss a new contract with him after their Challenge Cup win last season.
Plummer told the Hull Daily Mail that the decision was taken because of a "very average" run of league results, with Hull losing four of their last five.
"The board will never forget the cup success," said Plummer. "But results since have not been impressive. In fact, very average and you have to ask why and are we progressing?
"At the start of the season we set certain objectives, which we now feel we are in danger of missing out on.
"We have to look at the reasons for that, especially as we effectively have the same set of players. You can't win Super League without being consistent.
"We showed in winning the cup that we were capable of beating the top sides. It wasn't as though we had one good day.
"That cup form hasn't come out in the league. So why? You'd probably have to say we're under-achieving. Having looked at the situation we think changing it is the right thing to do."