Knox was born to Colin and Sally Knox in 1989. He was a pupil at Beths Grammar School, Bexley. He had been acting since the age of 11, and his first credited role was a small part in an episode of the ITV police drama The Bill and he also appeared in the Channel 4 reality show Trust Me I’m a Teenager, and the BBC comedy After You’ve Gone. He had previously appeared as an extra in a number of productions. The first film Knox appeared in was King Arthur in 2004. He also appeared on Tonight with Trevor McDonald. In 2007, casting began for the role of Marcus Belby in Harry Potter and the Half-Blood Prince, the film adaptation of British author J.K. Rowling’s best-selling novel and the sixth instalment of the Harry Potter film series. Knox posthumously starred in Harry Potter and the Half-Blood Prince (2009). Although his character does not appear in the seventh novel, Knox had signed on to reprise his role as Marcus in the final instalment of the Harry Potter film series, Harry Potter and the Deathly Hallows. The film was divided into two parts for financial and scripting reasons; Part 1 was released in November 2010, with the second part in July 2011. Knox died at the age of 18 after he was stabbed outside the Metro Bar in Sidcup, South East London, on 24 May 2008. He had intervened in a fight to protect his 17-year-old brother Jamie, who was being threatened by two men, one of whom was armed with two knives. Warner Bros. released a statement concerning his death: “We are all shocked and saddened by this news and at this time our sympathies are with his family”.