Rob Knox who plays the role of student Marcus Belby in the upcoming Harry Potter And The Half-Blood Prince was fatally stabbed outside Metro bar in Southeast London on Saturday morning.

The BBC reported that Knox, 18, was allegedly trying to defend his younger brother Jamie from a man armed with knives.

According to the BBC, as of Monday, police were still questioning a 21-year-old male suspect.

"Rob was kind and thoughtful and would always help out others- he would always spent his last penny on other people instead of himself," Knox's parents, Sally and Colin said in a statement Sunday. "The life and soul of the party, he was very outgoing loved sports and would always strike up conversation with people.

"He was respectful to others and adored by all his family and friends. He was an asset to the family."

Knox had just completed filming of the latest Harry Potter (which is due to be released in November) and had signed on to appear in Harry Potter And The Deathly Hallows, the seventh film in the franchise. He had been acting since the age of 11.

"We are all shocked and saddened by this news and at this time our sympathies are with his family," Warner Bros. Studio, which produces Harry Potter movies said in a statement.