When Harry Potter and the Half-Blood Prince is released this week in the US, it will be a bittersweet time for the family of actor Rob Knox, who was murdered TWO DAYS after he finished filming

Rob Knox, 18, played boy wizard Marcus Belby in The Half-Blood Prince and is seen around a dining table with co-stars Harry (Daniel Radcliffe), Hermione (Emma Watson) and Prof Slughorn (Jim Broadbent). In the photo from the new movie, Knox can be seen second from left.

Knox was stabbed to death by thug Karl Bishop, 22, outside a bar in Sidcup, South East London last May. The actor was defending his younger brother when he was attacked by Karl Bishop, who is now serving four life sentences for the murder.

Cast and crew from the film will wear white ribbons on their wrists at the movie’s world premiere as a mark of respect to the actor. Daniel Radcliffe said Knox’s death had hit the entire cast pretty hard. ‘I won’t pretend I knew him incredibly well, or was his best friend on set, but I knew him and liked him, and what happened to him was obviously tragic and awful,’ he said. Co-star Bonnie Wright, who plays Ginny Weasley – younger sister of Harry’s best friend Ron – said the cast wanted to show solidarity with all victims of knife crime. ‘It’s going to be quite a traumatic experience for his family, who’ve been very supportive of him. Obviously it’s going to be quite difficult, going to see him in the film,’ she said. ‘We wanted to wear as a mark of respect a white ribbon, not only for his life but for other families who have experienced this traumatic crime.’