It is said that 18-year-old Knox, who will be seen on the big screen as wizard Marcus Belby, sustained multiple stab wounds on Friday night (May 23) after becoming involved in an argument with two armed men who had threatened his 17-year-old brother Jamie.
The whole incident had started because of a stolen cell phone and took place at the Metro Bar in Sidcup, Kent, where besides the young actor, four other men were stabbed.
Knox was immediately rushed to the Queen Elizabeth Hospital in Woolwich, southeast London, but was pronounced dead on arrival.
The police have started their inquiries into the murder.
'At this early stage, we retain an open mind as to any motive, and inquiries continue to establish the full circumstances of the incident. We do not believe the incident is gang-related,' Contactmusic quoted a spokesperson for the authorities as saying.
Meanwhile the executives at Warner Bros. Studio, which produces the Harry Potter movies, released a statement expressing their condolences to Knox's relatives.
'We are all shocked and saddened by this news and at this time out sympathies are with his family,' the statement read.
In the picture: Colin, Jamie and Sally Knox, respectively father, brother and mother of the 18-year-old actor walk after a press conference on Sunday in Sidcup, Kent.
Text: ANI | Photograph: Getty Images