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In this exclusive look at the Blu-ray/DVD extras of Katy Perry: Part of Me, debuting September 18, Katy uncovers her grandmother's racy past.

VIDEO: Katy Perry Retraces Her Journey in Upcoming Film

"I made G-strings for [showgirls]," said Katy's 90-year-old grandma, Ann Hudson. "I made all kinds, and I had a little pocket right here for those that wanted to take their rings off but didn't want to leave them in their dressing room."

Katy appeared shocked and captivated by the stories told by her grandma, whom the 27-year-old singer is clearly proud of. So much so that Katy would invite her grandma to appear with her during a live concert.

The DVD/Blu-ray features over an hour of never-before-seen footage of the superstar on and off stage. Those sold in the 48 contiguous United States will also include a Pink Ticket, allowing fans a chance to win prizes including a meeting with Katy herself.

Katy Perry: Part of Me is also available for On Demand and Digital Download starting tomorrow.