Despite organisers issuing a strict warning to attendees earlier this week over the 55th annual awards' dress code, Katy threw caution to the wind in a plunging gown.
The singer showed off her assets in a revealing green frock as she walked the red carpet outside the Staples Center in Los Angeles.
And here was us thinking it would be Katy's best friend Rihanna who would be first to flout the rule.
Katy turned up to see if she had walked away with the award for Best Pop Solo Performance for her song 'Wide Awake', but lost out to Adele.
MORE GRAMMYS 2013: