Has Katy replaced Rihanna to make Nicki her bestie?

We think these three musical mamas could all be BFF, but sources are saying there's an odd girl out and it's Rihanna! You see, even though Katy and RiRi used to be tight, insiders say they don't speak much anymore, but it's totally obvious to see that Katy and Nicki talk A Lot! In fact, the girls are always tweeting each other and shouting out their friendship on Instagram. "I like her whole attitude," Katy dishes about Nicki. "I think she is amazing and I love her sense of style." So, did Nicki officially replace Rihanna as Katy's friend? Not yet- we're holding out hope for all three girls to bond (and record a song together, perhaps?)!