The pair were said to have fallen out last October over Rihanna's decision to reunite with her abusive ex, Chris Brown and are reportedly still not on speaking terms.
Their refusal to sit near each other at the Grammys apparently angered event organisers, with a source telling US Weekly: “Such a headache! They aren’t tight anymore because Katy doesn’t approve of Rihanna dating Chris Brown.”
However, HollywoodLife.com reports friends close to Rihanna are insisting she has no problem with Katy, but does not care what she thinks about her relationship.
Rihanna and Katy were last seen together at the MTV Video Music Awards in September, which was also the night RiRi was caught sharing a kiss with Chris.
But the 'California Gurls' singer warned her pal she was 'making a huge mistake' by getting back with Chris.
A source told New York Daily News at the time: “They’re barely talking and ever since the couple reunited, there has been tension between them. Katy has been spending a lot of time with pals Robert Pattinson and Kristen Stewart.
“Katy fears Rihanna is making a huge mistake and doesn’t want to be part of it.”