Why Did Katy Perry Miss Rihanna's Birthday Bash?

Songbird is absent from Rihanna's birthday blowout but sends her love via Twitter...so what A-listers did attend?

Rihanna's birthday party was full of famous faces, but one was MIA: her bestie, Katy Perry.

A slew of stars such as Zac Efron, Ryan Phillippe, Jay-Z, Diddy and Snoop Dogg hit the private L.A. bash Sunday night, but Katy was too busy elsewhere.

Was she trying to get back at Rihanna for missing her wedding?

Hardly!

Katy was busy kicking off her California Dreams tour in Portugal, but still sent RiRi some birthday love across the Twitterverse.

"happy birthday boo. Wish I could b there to blackout! Luv U!" Katy tweeted Sunday as Rihanna was partying after she performed at the All Star Game.

The birthday girl totally understood, replying back "bitch are u kidding? I missed ur WEDDING!! This is small stuff boo! #whenworkcalls".

Good to see all is well between two of our favorite fierce females!

Back at Ri's bash, the birthday girl ate Sprinkles cupcakes and even smoked cigars!

"Camacho cigars had a hand-roller there personally rolling cigars for celebs," a source tells E!, "Rihanna was smoking hers while drinking champagne straight from the bottle!"

Sounds like a good time to us!