Nicky Hilton is rumoured to be dating Mary-Kate Olsen's ex-boyfriend - just days after sister Paris was linked to another of the pretty twin's former lovers. The sexy socialite was spotted out with David Katzenberg, who dated Mary-Kate for nine months last year, at her 22nd birthday party in West Hollywood. The twosome were joined by Paris and her new love interest, Stavros Niarchos, who also used to romance Mary-Kate. Following her split from her shipping heir fiancÃ©, Paris Latsis, the hotel heiress hooked up with her second wealthy Greek, whose family is worth a staggering $75billion.Last year, Nicky annulled her Las Vegas marriage to Todd Meister. The couple, who met in 2003, stunned friends and family when they announced they were to tie the knot at the Las Vegas Wedding Bureau and Vegas Chapel after a night out partying.They had began their evening with friends at the trendy Palms Hotel and Casino Resort before taking everyone by surprise by announcing they were to marry later that night. However, the later decided to have the marriage annulled because it was "beyond solid"