A 22-year-old British man has been found guilty of murdering Harry Potter actor Rob Knox, according to BBC News. Karl Bishop was convicted of stabbing the 18-year-old five times outside the Metro bar in South East London almost a year ago. Bishop pleaded not guilty to the murder, saying that Knox had attacked him and he had been acting in self defence. He was sentenced to life imprisonment and told that he will spend at least 20 years behind bars. Knox, who had just finished filming his motion picture debut in the role of Hogwarts student Marcus Belby in the upcoming Harry Potter And The Half-Blood Prince, died as he attempted to protect his younger brother from Bishop. “Unhappily, his courage and his sense of duty were to cost him his life,” said prosecutor Brian Altman. Bishop was also found guilty of wounding Knox’s friend Dean Saunders, who escaped with his life.