Born a girl but identifying as a boy, Donnie Collins has found his band of brothers in the unlikeliest of places — a college fraternity.

After his insurance company refused to pay for his gender transition surgery, Donnie’s Phi Alpha Tau frat at Emerson College raised the cash in just two days.

It’s turned into a social media sensation for the 20-year-old sophomore.

“I never thought of myself as a person who could join a fraternity,” said the screenwriting major. “I just remember thinking, ‘I’ve never seen so many people in one room that I wanted to have in my life.’ ”

Toss out the stereotypes of beer-guzzling frat initiations. Phi Alpha Tau welcomed the transgender pledge a week ago and posted a YouTube appeal to a fund-raising page for their new brother almost immediately. As of this afternoon, the frat had raised $17,000-plus for “top surgery” for Donnie. He needs only $8,000 for the chest reconstruction. The rest will be donated to help others like Donnie.

“For me, medical transitioning has been so important because it just removes that aspect of confusion and depression from my life,” said Donnie, who has struggled since middle school with his gender identity.

“Right now I’m wearing five layers … plus this jacket, so even when I’m casual, I’m not really casual,” he told the Herald yesterday about “compressing” his chest. “It’s a lot to handle … it’s a lot to handle.”

Donnie said he’s been depressed about his body for too long and tired of fighting a losing battle with his insurance company.

But his frat brothers helped lift that burden.

“You feeling OK?” Phi ­Alpha Tau fraternity brother, Christian Bergen-­Aragon, asked Donnie yesterday outside an Emerson high-rise dorm on Boylston Street.

“I’m functioning,” he replied with a smile.

Donnie was eating cupcakes and guzzling Gatorade yesterday afternoon as his quest went viral. The Virginia native was worried he would have to take out loans to pay for the surgery. His brothers wouldn’t stand for it.

“To me this is a true demon­stration of what brotherhood should be about,” said Jason Meier, Emerson’s director of student activities. “Hopefully this will start to help change some stereotypes about Greek life”

Donnie said his next step is a hysterectomy — but that’s a serious step for down the road.

“I started to realize, my whole life I would have been so much happier if I had been a boy,” Donnie said.

“I just feel great that like, the issue is visible,” Donnie added. “And it’s more than just like about my surgery and more about an amazing representation of what some members in Greek life can do.

“I’m really just so moved by everything right now that I don’t know what to say.”