The 28-year-old singer grew close to Kristen's ex-boyfriend Robert in the wake of their split in June, and Katy wanted to tell Kristen that nothing was going on between the pair and she was just being a good friend to the heartbroken actor.
The 'Part of Me' hitmaker insists their friendship wouldn't have been an issue if she didn't have breasts.
Speaking to the new UK issue of ELLE magazine: ''I sent her a text message saying,' 'I know you've seen all this stuff but you know I would never disrespect you. I'm not that person. I'm just trying to be a friend to him but it is unfortunate that I do have a set of t*ts.'''
Rumours of a romantic attachment between Katy and Robert became rife after the pair were spotted at a Bjork performance at the Pantages Theater in Los Angeles in June.
This came shortly after the British star spent a week at Katy's house following his split from Kristen who he dumped after four years together for a second time after discovering she was back in touch with 'Snow White and The Huntsman' director Rupert Sanders, who she had an affair with last year.
Katy was previously married to British comedian Russell Brand but they split in December 2011 after 14 months of marriage and their divorce was finalised in July 2012. She has since embarked on a relationship with musician John Mayer.
Both Robert and Kristen have remained single since their split.
Katy also discussed her close friendship with Rihanna in the magazine interview, describing her as a shining ''light'' in her life.
She said: ''I love her (Rihanna) and every time I see her, I'm reminded of the light that she has. There's a lot of dark in this business. I know a lot of people out there with the most detrimental entourages - they are the root of their demise. It's really unfortunate but you can't save these people. My days of celebrity saving are over!''
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