Pop star Kevin Jonas was initially hesitant about the success of a Jonas Brothers comeback because he was worried their fans had outgrown the band.

The sibling trio began formulating reunion plans last year (18) and made its chart return in March (19) with the hit single Sucker, earning Kevin, Nick and Joe their first number one on the U.S. Billboard Hot 100.

On Friday (07Jun19), they dropped their first album in a decade, Happiness Begins, days after the premiere of their new Amazon documentary, Chasing Happiness, which charts the group's rise to fame, its 2013 split, and its reunion.

They are also set to embark on a months-long tour and launch a memoir, titled BLOOD, later this year, and the huge demand for the Jonas Brothers' return has really taken Kevin by surprise.

"Last year, he was like, 'Do you think anyone will care?'" Joe recalled of their initial conversations about getting the band back together.

They celebrated the release of Happiness Begins by taking over New York's Rockefeller Plaza for an early morning gig on Friday as part of America's Today Show Summer Concert Series, and looking out at the huge crowd filled with fans singing along to every word of their songs left Kevin astounded.

"It's amazing, it's a little surreal," he confessed onstage. "I never thought this would happen again for us as the (Jonas) Brothers, but to be back, having this album out, and being here with everyone today, it's incredible."

The stars also toasted the project's launch at a Spotify-sponsored carnival gig in Brooklyn on Thursday night, when Kevin's two young daughters, Alena, five, and two-year-old Valentina, got to watch their dad perform professionally with Nick and Joe for the very first time.

"Last night was the first time they came to a small intimate show and I couldn't do anything but watch them," the musician smiled. "Seeing them dance, seeing them sing, I am their biggest fan and I love the support from them."

And Uncle Joe cannot wait to have the girls join them on tour: "It's gonna be a blast, I mean, we're gonna have the nieces out (on the road), it's gonna be so fun," he gushed. "Last night, they got to see him (Kevin) play for the first time ever, and it was just a dream to watch that in real life."