LONDON: Niall Horan has successfully undergone major knee surgery . The One Direction star has asked fans to respect his privacy as he starts to recover from the operation but he refused to go into detail on the matter. Writing on Twitter, he revealed: ‘’Hey guys I know most of you have seen those pics today. ‘’But I would like to tell u, it was a complete success, considering the scale of it. So all I ask of you is that you would respect my privacy as I try to recover and get for the where we are tour.–EY