We don't know about you, but this makes us very sad indeed.
And true say, at the Grammys neither said a word to each other on the red carpet or throughout the ceremony.
It is also believed that Katy went out of her way to put in a special request to not be seated anywhere NEAR her former pal.
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So WHY are the former chums no longer on speaking terms? Well, it's all down to blimmin' Chris Brown (why are we not surprised?).
It's reported that Katy was so unhappy with Rihanna's decision to reconcile with her ex that she couldn't continue their friendship.
A source told USMagazine.com: "They aren't tight anymore because Katy doesn't approve of Rihanna dating Chris Brown."
Katy, 28, is believed to think that Rihanna, 24, is making a 'huge mistake'.
And after Chris Brown was arrested for assaulting Rihanna back in 2009, we can kind of see where Ms Perry is coming from.
However, chums of Rihanna would seem to disagree, saying Katy should be happy as long as her friend is happy.
An insider told HollywoodLife.com: "Rihanna doesn't have a problem with anyone and could give a f**k about what anybody thinks about her relationship."
Well, that's that then we suppose.
We just hope the pair manage to make friends eventually, water under the bridge and all that?!