It came like the slow ripping of a Band-Aid, and now the wound will bleed out all over Islanders fans for years to come.

A dark day in Islanders history arrived Sunday when captain John Tavares decided to become a free agent and then sign a sentimental deal with his hometown Maple Leafs. The seven-year, $77 million contract, absurdly loaded with lockout-proof signing bonuses — only $6.11 million of the $77 million is salary, but the annual salary-cap hit remains $11 million — is still assuredly less than what the Islanders were offering.

First is the fact that the Isles were the only team able to give him eight years before the clock struck midnight Saturday. It is also believed that their offer was around (if not above) $12 million per year.

Tavares, who will turn 28 by the time the season starts, grew up in Mississauga, Ontario — a half hour outside Toronto — and he tweeted a picture of himself as a child sleeping in a bed of Maple Leafs sheets, adding the caption: “Not everyday you can live a childhood dream.”

It was a brutal body shot to the Islanders, who have been doing their best to rebuild the franchise from the top down, starting with the recent hirings of president Lou Lamoriello and Stanley Cup-winning coach Barry Trotz. They have secured the right to build a new arena at Belmont Park, set to open for the 2021-22 season, and even their draft last weekend went better than expected.

But last week, Tavares had all six of his suitors out to his agent’s office in Los Angeles, hearing pitches from the Islanders, Leafs, Sharks, Stars, Bruins and Lightning. He then flew back to Toronto on Thursday, and broke the news himself Sunday afternoon on Twitter, saying thank you to the Islanders fans who supported him.

He reiterated those comments later with a heartfelt press conference in Toronto, where his voice had the slightest bit of tremor when discussing the fan base of the franchise that took him with the No. 1-overall selection in 2009.

“That place means a lot to me,” Tavares said. “Everything I’ve been through there, the impact people had on me, the things we went through as a group, the teammates I had there — it was such a hard decision because of how special it was. It’s a great organization, tremendous fan base, tremendously loyal, tremendously passionate. You ever been to a game with Islanders fans? It’s really unique. I think my message was what I put on Twitter today, some things that came from my heart. And to reiterate, I just want to say thank you.

“I know it’s a bittersweet day there,” he added, “but I really think the future is bright.”

Tavares — a five-time All-Star who twice finished third in the Hart Trophy, awarded to the NHL’s MVP — leaves the Islanders fifth on their all-time scoring list with 621 points behind Bryan Trottier, Mike Bossy, Denis Potvin and Clark Gillies, who all spent at least a decade on the Island. But he also leaves with just one playoff series victory in three playoff appearances.

The Islanders organization bent over backwards to try to accommodate Tavares, who could have signed an extension back on July 1, 2017. But he wanted to explore his options, and the Islanders did him a huge favor in agreeing to not trade him before the Feb. 26 deadline. Garth Snow, the general manager at the time who has since been relieved of his duties by Lamoriello, was part of the decision-making group that allowed that to happen, at the behest of principal owner Scott Malkin. But now the club has nothing to show for it as it tries to regroup.

“The New York Islanders would like to thank John Tavares for everything he has done for the franchise throughout the past nine seasons,” Lamoriello said in a statement. “John has achieved great individual success on the ice, as well as devoting a tremendous amount of his time and energy to the community. We wish him and his family all the best.”

That is not going to be the sentiment from the fans, who likely have already circled Feb. 28, with the Leafs at Barclays Center, for a day of peak vitriol. But the decision also leaves the Islanders with a ton of salary-cap space, and Lamoriello as the man to find a way to make them competitive again — even without one of the best players in the world as a cornerstone.

But this was still a dark day in franchise history, one to be remembered for the difficult decision that bloodied the Islanders organization and those who support it.

“I just felt my heart was in two places,” Tavares said. “My gut was tearing apart trying to figure out what I wanted to. I just felt this opportunity was so rare.”