The long-running London pop radio station packs an eye-watering number of huge names into Wembley Stadium for their annual all-day megashow. As well as homegrown talent like Robbie, Olly and Jessie – plus Ellie Goulding, Labrinth, The Saturdays, Rizzle Kicks, Wiley, The Wanted, Lawson, Charlie Brown and talent show breakouts James Arthur, The Loveable Rogues and Union J – they're jetting in US megastars Taylor Swift and Will.i.am and (perhaps most excitingly) South Korean global sensation Psy. And it's not all your typical pop stuff too: Rudimental, Duke Dumont, Disclosure and AlunaGeorge are all present to represent the UK dance underground as it continues to cross over into the mainstream. Oh, and the whole thing is hosted by Justin Timberlake. Obviously. The event is officially sold out, but if you do want to sample this taster menu of global pop talent there are plenty of tickets being resold online.