The Prince and Princess of Wales are said to have a 'naughty' secret weapon that they use to help keep their high-profile marriage on track. The royal couple tied the knot in Westminster Abbey in April 2011 and have gone on to welcome three children together. Given their global status, all eyes are on William and Kate when they step out in public. But behind the scenes, their relationship is incredibly relatable. According to one expert, the couple's playful side is their secret weapon – and it'