With a robust “Hello, Brooklyn!” Islanders owner Charles Wang announced that the New York Islanders are moving to the Barclays Center in Brooklyn.

Wang, joined by Mayor Michael Bloomberg, Bruce Ratner, developer of the Barclays Center, and several other officials, said the Long Island-based team signed a 25-year agreement and will take to the ice in Brooklyn starting in 2015.

“When the Islanders came into existence in 1972, they shared the Nassau Veterans Memorial Coliseum with the New York Nets,” Wang recalled, “and this announcement today reunites these two franchises.”

The newly opened 18,000-seat arena already hosts the Brooklyn Nets team, currently playing pre-season games. It will host the season opener between the Knicks and the Nets next week.

Like the Knicks, the Islanders’ hockey rival, the New York Rangers play at Madison Square Garden. Bloomberg noted the move means the rivalry between the Islanders and NY Rangers just got bigger.

And he’s hopeful that Brooklyn will help bring the “mojo back” for the four-time Stanley Cup champions.

“The whole world knows that Brooklyn is big time and now we’ve got the big league sports to prove it,” he said.

He added the move would help add more jobs at the arena, as well as the surrounding area, which “will mean millions of dollars in new tax revenue, the city will be able to pay for schools and police officers, and everything else we need to keep our city growing.”

But the city’s gain is Nassau County’s loss.

Wang said a major goal was to keep the team local and they tried to keep the team in Nassau County, but “unfortunately we were unable to achieve that dream.”

He told Nassau County Executive Ed Mangano of his decision Wednesday morning.

Last year, voters in Nassau County defeated a plan that would have allowed the county to use $400 million to redevelop the 40-year-old crumbling stadium.

Mangano took to twitter to say his administration worked hard to retain the Islanders. "I have supported various proposals to redevelop the HUB, including a public referendum in which voters chose not to construct a new sports arena." He added he will select an economic development team to help redevelop the Hub into "a vibrant destination and job creation center."

Supporters of the redevelopment said the county stood to lose $243 million a year and more than 2,000 jobs if the Islanders leave and the Nassau Coliseum closes.

Like any good new neighbor, though, Bloomberg brought a housewarming gift for Wang and the team’s general manager: MTA cards. He said he hopes they use it to travel to the Canyon of Heroes for the Islanders Stanley Cup championship parade.

But only after 2015.

Andrea Bernstein contributed reporting

Watch a video of the announcement below: