How sweet! Rihanna helped celebrate the release of Katy's new single, 'ROAR' last night at the Lion in New York City.

Rihanna made a surprise appearance at the pre-release party (where John Mayer was also in attendance) for Katy's third studio album 'Prism,' which drops Oct. 22, and later posted the photo above to Instagram along with the tweet:

It marked the first time the two singers have been seen in public together since last year's VMAs. Their friendship reportedly cooled because Katy was none too pleased her longtime pal got back together with Chris Brown -- but now that that's over (again and for good, we hope), it looks like the ladies are BFFs once more.

Maybe Katy can return the love when Rihanna's second fashion collection for River Island launches next month. The 80-piece collection is described as a mix of "urban sports lux with sophisticated chic," and includes items like skirts, jumpers and a range of underwear.

"I literally designed everything I want to wear, exactly how I want to wear it," Rihanna said. "We're giving it a New York street vibe."

The Autumn/Winter 2013 collection launches a "first wave" on Sept. 12, with a "second wave" due in November.