Here’s one way you know that Florida Georgia Line and Backstreet Boys’ alliance is a genuine one: It seems like no sane manager or label executive would have suggested it.

Who in their right mind would urge a red-hot country duo to join forces with a veteran boy band, of all acts? Meanwhile, that boy band’s team had recently been setting its sights on a residency gig in Las Vegas, not chart success in Nashville.

Instead, this out-of-nowhere partnership came directly from the groups themselves, after they’d forged an unexpected, real friendship. And perhaps that’s why it’s been a huge success.

This year, their collaborative single “God, Your Mama, And Me” went platinum, and brought the Backstreet Boys back to Billboard’s Hot 100 chart for the first time in a decade. Together, they stole the show at April’s Academy of Country Music Awards, performing a mix of each other’s hits.

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They’ve spent their summer sharing the stage on a massive stadium tour, and they’ll do it again on TV this Wednesday with the premiere of their “CMT Crossroads” concert special (CMT, 9 p.m. Wednesday).

“After being in the business almost 25 years ... it's nice to have something like this,” says Kevin Richardson of the Backstreet Boys. “This was a surprise.”

But how did it happen?

Well, the seeds were planted back in the ‘90s, when Florida Georgia Line’s Tyler Hubbard and Brian Kelley were in middle school. The first concert Kelley ever attended was a Backstreet Boys show, and the group's CD was one of Hubbard’s first musical purchases. In their bar band days, they would open and close shows with a cover of “I Want It That Way.”

Last year, they were headlining a huge summer tour, in the wake of country smashes such as “Cruise,” “Dirt” and “H.O.L.Y.” That’s when they started sheepishly admitting to their audience that they grew up listening to the boy band.

“Don’t laugh!” Hubbard said to an audience member at an early tour date.

But while the crowd was still laughing, Hubbard and Kelley would launch into a fearlessly fun cover of “Everybody (Backstreet’s Back).” It brought the house down every night.

The Backstreet Boys quickly caught wind of this. The group’s Nick Carter says they all crowded around to watch video footage on social media, and tried their hardest to hear if the country audience really was enjoying the song.

Soon, Carter was hanging out with the duo at the CMA Music Festival in Nashville, and they played him an early version of “God, Your Mama and Me.” In a matter of weeks, it turned into a collaboration.

But the bromance between these two acts hit a new peak in April, when they performed “Everybody” together at the Academy of Country Music Awards. Before the show, Hubbard and Kelley made a surprising request: They asked the Backstreet Boys to teach them their choreography, so they could all dance on stage together.

It was a bold choice, and there were palpable nerves backstage before the performance.

“We were scared,” says Backstreet's Howie D. “We didn't know if they were gonna be like, 'Get these boys off the stage.’ ”

They weren’t. The moment Hubbard and Kelley fully let their guard down and busted a move, the crowd went wild — particularly Tim McGraw, whose jaw-dropping reaction went viral on social media.

It was a fitting prelude to their summer stadium tour, where each show ends with all of them onstage with rapper Nelly, performing “Cruise.”

“It's the best closing song of any show, I'm telling you,” Carter says.

Adds Hubbard: “It takes every ounce of energy I have not to crowd surf every night.”

That’s where our interview falls off track for a minute, as everyone shares their crowd-surfing war stories. The real rapport between these guys is obvious. It’s also clear that the collaboration’s success has really meant a lot to the Backstreet Boys, now 25 years into their career.

“When this happened, for me, it was just like this revitalizing in my soul,” says Brian Littrell. “To really become a fan again, of good songs, and good music, and giving me something to aspire to.”

“People come and go in this business, and friendships are kind of hard to hold on to,” adds A.J. McLean. “But when something fits as naturally as this friendship now does, we're gonna be family and friends for eons. It just works.”

"CMT Crossroads" with Florida Georgia Line and Backstreet Boys premieres at 9 p.m. Wednesday on CMT.