Still reeling from the loss of grandmother Clara "Dolly" Braithwaite, Rihanna has pulled out of the Rock In Rio festival in Madrid, Spain, Contact Music reports. The R&B superstar had been slated to headline Thursday's (July 5) concert, and as organizers look to book a replacement, they're offering refunds to disappointed fans.

Ri's Rio cancellation comes on the heels of what, by all accounts, was a wildly unfocused performance at Sweden's Peace & Love Festival this past weekend. The singer had an excuse -- she'd just learned of Dolly's death -- but some concertgoers walked out on her set, believing she was intoxicated.

The singer took to Twitter soon after to pay tribute to her beloved "gran gran," who she visited regularly in New York.

''Goodbye #grangranDolly get your beauty rest until I see you," she tweeted, adding, "#grangranDolly that is all.''

Rihanna is, however, still scheduled to take the stage this weekend at the Wireless Festival in London.

See Photos of Rihanna Walking the 2012 Met Gala Red Carpet

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