FAIRFAX, Va. -- Think Syracuse in the Big East. Or Maryland in the Atlantic Coast Conference. That's the sort of emotional tie George Mason had with the Colonial Athletic Association, helping launch the mid-major conference in the 1980s and making it part of basketball lore with a Final Four run in 2006.

That's why athletic director Tom O'Connor called it a "bittersweet" day Monday when he announced that the Patriots were moving to the Atlantic 10, the latest fallout from the ever-shifting conference alignments in college sports.

"That was a difficult phone call to make last night," O'Connor said. "There is a lot of sentiment involved, a lot of personal relationships involved. ... But we have to move on, and we have to move on with business."

George Mason will join the A-10 on July 1, the same move made by Virginia Commonwealth last year and by Richmond more than a decade ago, while also forming a subway conference rivalry with nearby George Washington. The CAA isn't what it used to be, so it was worth the $1 million exit fee and the minimum of $1.65 million in conference payouts that the GMU will forfeit, money that university President Angel Cabrera said the school will recoup in the A-10 "in as little as five years."

The CAA will be down to nine schools in 2013-14, with Old Dominion (Conference USA) and Georgia State (Sun Belt) departing for more football-centered conferences.

"The landscape has changed in collegiate athletics," O'Connor said. "What's exciting about this move is it brings us back to two rivals that were in the CAA with us, VCU and Richmond. ... Once ODU and VCU made their move, and Georgia State made their move, and there were other movements in the country, then we looked at our program and where we wanted to go, and we felt that now was in the best interest."

George Mason, which doesn't play football, goes from one basketball-centric league to another -- one that is also struggling to keep members. Butler and Xavier are leaving the A-10 in July to join a splinter group that is reforming a basketball-focused Big East, while Temple will join the Big East's football-focused members in a yet-to-be-named conference. Charlotte is heading to Conference USA, also because of football.

Adding George Mason puts the A-10 at 13 schools for next season, "which, quite frankly, is still quite a large conference," said A-10 Commissioner Bernadette McGlade.

"The numbers of institutions is not necessarily the be-all and end-all," McGlade said. "It's what institutions make up the Atlantic 10."

The CAA, meanwhile, will have to rebuild itself yet again. The conference was near collapse in 2000 -- down to just six teams -- before an influx of new members and a period of unprecedented prosperity surrounding the Final Four runs by GMU and VCU.

"We're going to stay viable. ... We'll be fine," CAA Commissioner Tom Yeager said. "We've had two Final Four appearances since the last apocalypse."

But, when asked if all the shuffling had taken the fun out of the job, Yeager answered: "Well, I'm glad I'm 62 instead of 42 right now."

"I think I can speak for all the commissioners -- this is something that I don't think any of us enjoy," he added. "However we react is going to impact somebody else, and, look, it's been going on all the way to just about all the leagues. I don't think any of us think this is the highlight of our career experiences by any stretch."

While the move provides a natural boost for George Mason's basketball team, the school's seven spring teams are now automatically banned from CAA championships this year. O'Connor met with those teams Monday morning and called it the worst part of the decision to switch conferences.

"It was agonizing," he said. "And I apologized to the athletes."

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AP Sports Writer Hank Kurz Jr. in Richmond contributed to this report.

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