Katy Perry is allegedly "incredibly angry" about Rihanna's renewed relationship with Chris Brown.
The 28-year-old pop star has been a close friend to the Barbadian-born chart-topper for some years.
Their friendship has now reportedly come to a bitter end following Rihanna's recent interview with Rolling Stone magazine, in which she confirmed she is back with her abusive ex-boyfriend Chris.
"Katy was always the one person who could really stand up to Rihanna," a source close to the star told British magazine Grazia.
"When it comes to Chris, Rihanna isn't willing to listen. Katy is still incredibly angry about what Chris did, and she doesn't believe he can change."
The demise of the two US pop princesses' friendship is said to have been in the works for some time. Katy is reportedly concerned about Rihanna's unstoppable hedonistic lifestyle and deeply fears for her health.
Friends say that Katy is so strongly against Rihanna's decision to try again with shamed star Chris that she has washed her hands of her completely now.
"She has stuck her neck out for Rihanna, and so it really hurt when Rihanna ignored her advice. Katy told Rihanna that she couldn't stick around and watch someone she loves make such a big mistake, and that she had to walk away.
They haven't spoken for months," the friend revealed. "Chris is like Rihanna's addiction and no one can talk any sense into her."