Sarah Michelle Gellar has fans convinced that she's her own daughter after she posted a throwback snap on Friday.MORE: Sarah Michelle Gellar reaches out to Buffy co-star with sweet birthday messageThe Buffy the Vampire Slayer star posted an old Burger King advert that she had been a part of back in the 1980s.The youngster was pictured holding a burger and a Pepsi, while wearing a white blouse with some red dungarees that featured a maple leaf in the middle."Throwing it back very far this