It's only fitting that in its 20th year, Scotland's biggest music festival should be graced by the presence of the world's biggest pop star.

Her newest album, Unapologetic, sets out her stall - she doesn't care what you think. Rihanna's rise to the top of the pop pyramid has been about combining naughtiness and disarming honesty, underlined by an addictive series of huge pop royalty collaborations, with David Guetta, Will.i.am and Scotland's very own superstar DJ Calvin Harris providing suitably massive grooves to give the Main Stage sound system a healthy workout.