Onstage at their Into the Millennium residency -- which began last month and wrapped its first wave on Sunday night (before kicking off 14 additional dates starting in December) -- Backstreet Boys promised to put the crowd into a "time machine" back to the late-'90s heyday of boy bands and bubblegum pop. Katie was in the orb for the 21st show on Sunday night, and on the new Billboard Pop Shop Podcast, she tells Keith all about her spaceship ride back to the turn of the millennium.

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