Jackie, Tito, Jermaine and Marlon may be the Jacksons performing onstage in their just-launched "Unity Tour 2012? reunion tour, but it's their late brother Michael Jackson who they say is still stealing the show.

"He's on stage with us in spirit as well," Tito said today on " Good Morning America," of Michael, the superstar who passed away three years ago this month. "It's very emotional."

WATCH: A Look Back at the Jackson 5

Long before N'Sync, the Backstreet Boys, One Direction and Justin Bieber, there were the Jackson 5, the chart-topping, synchronized-dancing, matching-costume wearing brothers who took the world by storm in the 1960s and '70s.

More than 30 years later the brothers are back, playing to packed houses on their just-launched "Unity" tour that will take them to more than 20 cities across North America this summer.

"What brought us back together was time and the fans," Jermaine told "GMA." "It's the music that gets us going."

The reunion marks the first time all four brothers have toured together since their 1985 "Victory Tour." Their set includes hits that led them to become the first group ever to have their first four singles hit number 1 on the Billboard Charts, songs like "ABC" and "I Want You Back," songs they've had to adapt in Michael's absence.

"No one can take Michael's part but we're doing a great job," Jackie said. "We're all sharing parts together."

"It's very hard," Jermaine said of their brother's absence. "You're singing these songs and all of a sudden something hits you."

The emotions will continue at the brothers' next performance, a sold-out show at Harlem's famed Apollo Theater where they say it all began.

"This was our launching pad," Marlon said of the legendary theater. "We used to come to amateur night at the Apollo and try to make a name for ourselves. So we wanted to come and give something back."

The brothers say they've been touched by the outpouring of support from their fans, most notably a very A-list music superstar, Beyonce, who penned a tribute to Michael on her website Monday that included a link to a YouTube video of the Jackson 5's live performance of "Who's Loving You."

"She's incredible," Jermaine said "It's a great feeling because we worked so hard. Our whole thing was to work hard and to achieve and I guess it shows. We're very happy that people have admired and loved the things we've done over the years."

"We thank our parents," said Marlon. "Our parents saw that we could entertain and know that we had enjoyed it so they made sure that we stuck with it and this was the outcome."

The brothers offered some of their own parenting advice to Michael's children, particularly his daughter, Paris, who has made it known she wants to continue in her father's footsteps as an entertainer.

" My whole thing is you're a child," said Marlon, echoing comments made by Janet Jackson, who publicly advised her niece to wait to start a career in show business. " Enjoy your childhood and once you become an adult you'll be an adult for the rest of your life, so enjoy your childhood. "