The former glamour model has hit out at her rival - despite calling her ''beautiful'' - by claiming she is ''fooling the consumer'' by hiding her real body shape in photo shoots.
Speaking on her FUBAR Radio show today (15.07.14), she said: ''I'm not having a pop at Kelly, because I think she's one of the most beautiful women around, but she does look quite curvy and she's always in the gym, but she's looking bigger than she normally does.
''When you look at her campaign pictures she looks amazing and it's fooling the consumer ... Why can't she show her real body off? I'm quite happy at photocalls standing there in my underwear.
''So why don't people like Kelly Brook stand there in her underwear and show off what she really looks like? Show it. She's stunning, she's a beautiful looking woman and she's got curves, so don't be afraid of it.''
Katie also offered her thoughts on Kelly's whirlwind romance with fiance David McIntosh - who she got engaged to in March 2014 after just a month of dating - and admitted she didn't think they'd go the distance.
She said: ''I don't think they'll last. Prove me wrong, I hope they do. I met him once, maybe twice. I don't really know him.''
Perry appeared on James Corden's 'The Late Late Show' on Monday and addressed her long-standing rivalry with Swift.