Rihanna and Chris Brown's reconciliation at this year's Grammy Awards on Sunday night, has stirred quite a buzz amongst their fans. But some of the couple's celebrity friends are not happy about their on-again romance either.

Katy Perry, who became close with the pop singer during last year's Grammys, "doesn't approve" of Rihanna's decision to reconcile with R&B singer Brown. And as a result, Perry and Rihanna's friendship has suffered, according to Us Weekly.

"They aren't tight anymore because Katy doesn't approve of Rihanna dating Chris Brown," an insider reportedly said about the two singers.

Both Perry and Rihanna did not want to sit next to one another at this year's Grammys, according to HollywoodLife.com.

Perry, 28, spent much of the evening next to her latest beau, John Mayer, 35. The singer's royal blue suit may have clashed with Perry's form-fitting, pale green Gucci dress, but the two also appeared cozy during the awards ceremony. The couple had the ideal front-row view of the night's performances.

Rihanna, 24, who won rave reviews for both her emotional performance of the ballad Stay with Mikky Ekko and her outfit--a flowing red gown designed by Azzedine Alaia--doesn't seem the least bit concerned with the outside opinions on her relationship.

A source close to Rihanna reportledly told HollywoodLife.com, "Rihanna doesn't have a problem with anyone and could give a f**k about what anybody thinks about her relationship. She was focused on her and Chris and enjoying her night." 

Rihanna and Brown appeared very cozy together throughout much of the ceremony.

The young couple carried on with their love-fest after the ceremony as well, drinking cocktails and becoming "very affectionate" as they whispered things into one another's ears throughout much of the night at the Zing Vodka Post Grammy Party held at Hollywood's Supperclub, a witness told Us.

Tags: Katy Perry Rihanna Chris Brown Grammys 2013