Rob Knox, right, with his mother, Sally, and 17-year-old brother, Jamie.

18-year-old Robert Knox, who plays Ravenclaw student Marcus Belby in the upcoming “Harry Potter and the Half-Blood Prince” movie, was killed outside a Sidcup, England bar early Saturday morning.

According to London’s Metropolitan Police, Rob Knox was stabbed to death just after midnight during a fight which sent five young men to various hospitals, including a 21-year-old man who has been arrested on suspicion of murder.

Witnesses say Knox died trying to protect his 16-year-old brother Jamie, who was attacked by a man with two knives.

In a statement, Rob’s family said he “was kind and thoughtful and would always help others out,” adding, “Rob… would always spend his last penny on other people instead of himself.”

“The life and soul of the party, he was very outgoing, loved sports, and would always strike up a conversation with people.

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

Warner Bros, the studio producing the film, also issued a statement saying, “We are all shocked and saddened by this news and at this time our sympathies are with his family.”

Friends leave flowers at the site of Rob Knox’s death in Sidcup in south-east England.

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