Many people meticulously plan weddings down to every detail - which usually means wedding crashers are far from welcome. After all, who would want uninvited guests taking up a precious seat at the venue or eating the expensive catered food? But, like with all things in life, there is an exception to this rule: celebrity wedding crashers. From Keanu Reeves to Serena Williams, these stars were welcomed with open arms by the bride and groom on their big day. In fact, they pretty much stole the show!