The 90th birthday bash for Nelson Mandela is taking place tomorrow, but hordes of Hollywood stars have already descended on London to honor the former South African president. The emcee for Friday's event, Will Smith, arrived with wife Jada Pinkett Smith for the pre-birthday dinner party at Hyde Park. They were joined by Oprah, Uma Thurman, Forest Whitaker, Kim Cattrall and Denzel Washington. And contrary to reports that supermodel Naomi Campbell was banned from introducing some of the performers following her airport arrest, her rep says that, "To my knowledge, she has always just been a guest." Singers Leona Lewis, Amy Winehouse, Annie Lennox and rock group Queen are slated to perform.