The Belfast Giants general manager Todd Kelman is leaving the club to become part of a Canadian consortium that is buying their Elite League rivals Cardiff Devils.
A Giants statement acknowledged that Kelman's decision would "come as a shock" to the club's fans and players.
Kelman has been at the Giants since 2000 when he was part of the club's first ever squad.
The Canadian was appointed general manager after his retirement in 2007.
Given Kelman's departure, recently-appointed coach Steve Thornton is now expected to assume the duties undertaken by the general manager.
"The appointment of Steve Thornton was part of the development planning for the Giants," said Robert Fitzpatrick, the Chief Executive of Giants owners the Odyssey Trust.
"Todd has kept me informed that he was exploring other options in relation to his future plans and whilst this has come a surprise, I am absolutely delighted that he is fulfilling his dream to be a part of owning a franchise.
"We are proud of what Todd has done as general manager and as a player and he will always be remembered fondly on and off the ice, we wish him well."
Thornton said that he excited about his increased responsibilities at the club.
"Although I was looking forward to renewing my working relationship with Todd, it was clearly explained to me that I was in charge of all hockey affairs and I have a vision for the delivery of that challenge," said Thornton.
"I am delighted to be inheriting a group of people including players, staff and volunteers with a great work ethic and a passion for this team who will be key to delivering on the plans we have."
Kelman helped the Giants clinch two League titles during his playing career at the Odyssey Arena.
His spell in charge of the club saw the Giants clinching two league titles including this year's triumph.
Kelman's move is more upheaval for the club after coach Paul Adey's surprise departure from the club in April a couple of weeks after guiding the team to the League title.
Thornton will not be able to call on the talents of winger Chris Higgins next season after the American opted to sign for Nottingham Panthers earlier this week.