Rihanna performed at the Wireless Festival London - Arab Today Fans at the the 2013 Yahoo! Wireless Festival were in for a surprise when US singer Rihanna joined Jay-Z for a performance on Sunday night at London\'s Olympic Park. The 25-year-old singer hit the stage with the legendary rapper and Justin Timberlake in the final headline slot of the three-day music event in Stratford, East London. Keeping her appearance under wraps, the performer sent the crowds wild when she walked on. Known for her edgy style, Rihanna definitely did not disappoint on the fashion front either. The singer rocked a tight black leather skirt and white bralet showing off her midriff. She accessorised with a diamond encrusted grill and a belly chain over her chic outfit.