After her own energetic performance thrilled the crowds, Katy Perry showed she is really a fan of BFF Rihanna, and joined the tens of thousands in the audience at 2:30am to watch her headline act on the opening night of the massive Rock in Rio festival in Rio de Janeiro, Brazil. And she seemed as captivated as everybody else as Rihanna delivered a string of hits with a sexy show. Pictured: Katy Perry