Hey, you know all those tabloid reports about Katy Perry and Rihanna not being friends anymore because Katy doesn't approve of Ri's relationship with Chris Brown ?  Well, they're not true.  How do we know?  Because Katy went out of her way to send Ri a lovely -- and profane -- tweet wishing her a happy 25th birthday.

Rihanna turned 25 on Wednesday, and Katy marked the occasion by tweeting , "HAPPIEST 25TH BIRTHDAY to my baby girl @ rihanna ! I wish I could b there drinking Mai-Tais & telling haters to eat a d*ck w/u!"

For her part, Rihanna tweeted a black-and-white photo of herself and Chris Brown from several years ago, and captioned it, " #throwbackRiRi my surprise 20th birthday party!! Im an old b**h now! Thank God for His gifts and His endless mercies! #25 #MilestoneLife ."

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