After helping bride-to-be Katy Perry celebrate her bacholerette party in Las Vegas last month, Rihanna was a no-show at her best friend's wedding in India this past weekend. So, what happened?

A source tells UsMagazine.com that Rihanna was just too busy adding final touches to her album: "Rih was finishing her album, and she just switched managers, so she had to pull out at the last minute.

"It was always sort of up in the air that she would go anyway, and Katy knew that. They saved her a room just in case, but they always knew it would be nearly impossible for her to make it as she's still finishing the album and it's out in a few weeks. Rih was in the studio all weekend," the source adds.