She has recently appeared to resolve her long-running feud with singer Taylor Swift.
But Katy Perry seemingly has another friendship she needs to mend, as it's reported Rihanna didn't invite her to her Met Gala afterparty at Up&Down in New York on Monday.
After not seeing each other for 18 months after a falling out, the pair - who were previously close friends - were also forced to awkwardly pose together on the red carpet.
Speaking of the said photograph together, a source told The Sun: 'Because Rihanna was chairing the Met Gala, she had to pose with a lot of the celebrity guests but it was really uncomfortable when she was asked to have the photo with Katy.
'They used to be close but Rihanna’s expression in the photo says it all. Katy was upset about the whole situation because Rihanna was cold to her and she wasn’t invited to her after-party,' it was continued.
MailOnline has contacted representatives for Katy and Rihanna for further comment.
This comes after Katy buried the hatchet with Taylor Swift after the pair feuded publicly for six years.
Taylor posted what looked to be a very private apology note to social media on Tuesday.
Swift - who has just begun her Reputation tour - wrote 'Thank you Katy' in red with pink hearts over the photo of the letter, and showed part of the writing.
It was difficult to see what Katy wrote but it looks like it said, 'I've being doing some reflecting on our miscommunications and though feelings between us .... would to clear the air ...deeply sorry for.'
However, Katy has reportedly been left 'upset' after Taylor posted the letter because the introduction suggests the brunette accepts 'full responsibility'.
'Katy expected that Taylor would post something about it,' a friend told The Sun Online. 'But she didn't expect the actual letter to go on social,' says her friend.
'The thing is, you can only see part of what Katy wrote and it looks like she's taking sole responsibility for the entire feud.
'Without context, it looks like she's taking the blame for everything and obviously there's a lot more to it than that.'
The singers have been embroiled in a feud since Taylor claimed the Bon Appetit singer stole three of her backing dancers from her Red tour in 2012.
In 2014, Taylor released the single Bad Blood, which was believed to be about her feud with Katy, and the star has seemingly retaliated with single Swish Swish, which is also reportedly about their battle.
'Thank you Katy': Taylor posted what looked to be a very private apology note to social media on Tuesday
Perry, who dates Orlando Bloom, said in 2017, 'Honestly, it's really like she started it and it's time for her to finish it.'
And Katy claims she 'tried to talk' to the blonde beauty about the feud some time ago, but revealed she 'wouldn't speak' to her.
Katy added: 'She wouldn't speak to me. I do the right thing anytime that it feels like a fumble. It was a full shut-down and then she writes a song about me and I'm like 'OK, cool, cool, cool. That's how you wanna deal with it?''
The hitmaker admits that her single Swish Swish is a direct 'reaction' to Taylor's, as she says the star has to learn about 'the law of cause and effect'.
She continued: 'But, what I wanna say is that I'm ready for that B.S. to be done. Now, there is the law of cause and effect. You do something and there's going to be a reaction. And trust me daddy, there's going to be a reaction. It's all about karma.'
© Associated Newspapers Ltd.