Many pop singers would have a hard time pinpointing the exact moment when they realized they had made it big. Not so with Nick Jonas, the youngest member of the boy band known as the Jonas Brothers. That would be Oct. 8, 2007, when he and his brothers took to the stage at the State Fair of Texas in Dallas.

"Fifty-thousand people showed up," recalls Nick, 15, setting one of the all-time attendance records for a Chevrolet Main Stage concert crowd. "It was like, 'Wow! This is going to be fun.' "

Just how much fun, even he couldn't have imagined.

In the months since, the siblings have gone on to become one of the hottest acts in 'Tweendom -- and not just because the boys are as cute as they are squeaky clean (devout Christians, all three wear purity rings, a sign they intend to practice abstinence). Signed to Hollywood Records, they ended up opening for Miley Cyrus on her sold-out "Hannah Montana" tour, rocked out at the 35th annual American Music Awards on Nov. 18, and last December performed in Dick Clark's "New Year's Rockin' Eve 2008" in Times Square.

Oh, and their self-titled studio album has sold more than 1 million copies since its Aug. 7 debut.

Not bad for three brothers who just a year before could barely pay the bills, according to a special collector's edition of People magazine.

Currently supporting Avril Lavigne on her tour across Europe, the siblings -- who found time to talk from their tour bus after a show in London, on their way to their next show in Ireland -- are about to get even bigger. At 8 p.m. Friday, the brothers will appear in the long-awaited TV movie "Camp Rock" on Disney Channel. And on July 4, they kick off their 30-plus-city "Burning Up" tour in Toronto, in which they'll promote their third album, "A Little Bit Longer," set for release on Aug. 12. The tour, which comes to the Post-Gazette Pavilion Aug. 26, winds up Sept. 5 in West Palm Beach, Fla.

They'll also star as secret agents in a new Disney Channel series called -- how do they come up with these things? -- "J.O.N.A.S.: Junior Operatives Networking as Spies." It goes into production in September.

"It's a crazy feeling," says middle brother Joe, 18, "It's kind of like when you're young and you decide to become an astronaut and you really do it. Our dreams actually came true."

"We're living the dream -- that's our slogan," Nick agrees. "We know a lot of people don't have what we have."

Given their escalating fame, it might follow that the brothers would sport equally expanding heads. But no; they're just as grounded today as they were growing up in Texas, to which they credit their parents, Denise and Kevin Sr., a former minister.

"We were raised in an amazing home," says Kevin Jr., 20. "Our parents were always so supportive."

If anything, they find all the adulation kind of, well, strange.

"Honestly, we look at each other and say, 'Why are they screaming? We're right over here,' " says Kevin, laughing. "But we love it."

That said, they enjoy meeting the fans that so enthusiastically support their expanding careers, whether it's on TV or in front of a microphone. Given their penchant for fashion, you may also soon see them at your local mall; boiling on the boys' stylish back burner is a desire to put out their own clothing line.

"We still get excited every day by what we do," says Joe.