TORONTO -- Maple Leafs president Brendan Shanahan says he knew once Kyle Dubas was elevated to general manager, an exodus from Toronto's front office was all but assured.

That shoe having now firmly dropped, the club finds itself with some big holes to fill.

The Leafs announced Tuesday morning that assistant GM Mark Hunter and the team had mutually agreed to part ways, and less than an hour later the New York Islanders confirmed Lou Lamoriello, who had recently shifted to the role of senior adviser in Toronto after three years as GM, will be their new president of hockey operations.

"It's always a sad day when you say goodbye to people that you respect and have worked with for a while, but it's something that certainly does not catch the organization by surprise," Shanahan said in a phone interview with The Canadian Press. "With every organization, there's people that are integral to the development for different stages. I think having those two guys aboard -- Mark for four years, Lou for three -- has been vital.

"Making the decision on Kyle, is really in my best assessment, what I thought was best for the organization going forward into the future."

The 32-year-old Dubas was promoted from assistant GM on May 11, a move that shuffled the 75-year-old Lamoriello to sidelines and saw Hunter, 55, passed over for a job he no doubt wanted.

"This was a likely scenario," Shanahan said of the departures. "What was most important to me was picking the person that I thought was ready to take the Leafs to the next stage of development."

Toronto's initial statement regarding Hunter made no mention of Lamoriello. The Islanders broke that news, thanking the Leafs in their release.

"We are committed to giving Lou every resource and the full support of the entire organization as we pursue our program to compete at the highest level," said Scott Malkin, managing partner of the Islanders.

The Leafs confirmed the Lamoriello move some 70 minutes after announcing Hunter had left.

Shanahan said Tuesday he could tell Lamoriello, who drafted him in 1987 when he was in charge of the New Jersey Devils, wasn't ready to fade away.

"Watching him in the last few months, it was my belief that if somebody made the right opportunity available for him, he was ready for a new challenge," Shanahan said. "I'm happy for him that he's taken one on close to his old stomping grounds, reuniting him with some people that he's worked with before."

Lamoriello was the Devils' GM and president of hockey operations from 1987 to 2015, a period that saw the team reach the Stanley Cup final five times and win the title in 1995, 2000 and 2003.

The Hall of Famer helped guide Toronto to a 49-26-7 record in his third season at the helm with young stars Auston Matthews, Mitch Marner and William Nylander in 2017-18 -- just two years removed from a last-place finish.

Lamoriello, whose son Chris has been New York's assistant GM since 2016, will immediately be tasked with trying to re-sign Islanders captain and pending unrestricted free agent John Tavares.

Hunter, meanwhile, joined the Leafs as player-personnel director in October 2014 before being elevated to assistant general manager in August 2016, sharing the role with Dubas.

At the time Lamoriello said the change in title was essentially "a formality as these are duties he's already been performing."

With both Lamoriello and Hunter now out the door, Dubas will get an opportunity to shape his own front office heading into his first season in the big chair.

Asked if the first-year GM needs experienced opinions in the room, Shanahan said there will be a collaborative effort to fill the now-vacated positions.

"It's got to be people that he's comfortable with and share his vision," Shanahan said. "(Dubas is) a smart young man and he recognizes some of the voices that have now departed."

Hunter was in charge of Toronto's pro scouting, amateur scouting and player evaluation departments. Dubas was GM of the American Hockey League's Toronto Marlies, overseeing all prospects within the club's system while also leading the Leafs' player development, hockey research and development departments.

Hunter, who played more than 600 games in the NHL, came to the Leafs in 2014 after helping build the Ontario Hockey League's London Knights.

Shanahan said Hunter, who can't work for another team until the middle of July at the earliest because of a non-compete clause in his contract, offered to stay on and work the draft for Toronto, but the organization declined.

"When Kyle and I took a step back and considered that, we decided that five weeks before the draft, it was probably better at this point to make a clean break," Shanahan said.