Katy Perry must not have gotten the dress code memo for the 55th Annual Grammy Awards, because her mint green Gucci keyhole dress made for a major display of décolletage.

We weren't shocked with the singer's wardrobe choice, since she usually leans towards the super-daring. However, we were surprised to hear the source of her outfit inspiration last night – Priscilla Presley in the '70s.

Long, flowy dresses, big hair ("The bigger the hair, the closer to God," Presley famously said), and keyhole necklines were certainly part of the actress' wardrobe repertoire, so we can see where Katy got her inspiration from. Click through the gallery to see some of our favorite '70s images of Priscilla Presley, and see how Katy's interpretation stacks up to the real deal.

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Photo Credit: Getty Images