Chris Martin, 21, a friend of Robert and others in their group including Dean Saunders, 21, said: 'It kicked off last week outside the Metro. It was over a mobile phone.
'Some bloke said to Dean (Saunders), "You nicked my phone."
'Dean said he hadn't and this guy smacked him in the face and gave him a black eye.'
Mr Martin, who is a regular visitor to the Metro Bar, said he did not recognise Mr Saunders' attacker among the 'mostly local crowd'.
Mr Martin said the man had gone back to the bar last night armed with two knives and had threatened to hurt Mr Saunders.
Rob was caught up in the ensuing fracas, he added.A 21-year-old man has been arrested for Rob's death. However, Robert Knox's stabbing death is not an isolated incident. Rob is the 14th teenage victim to die this year in Britain from a knife or gunshot injury. Another victim, Jimmy Mizen, was part of the same rugby club as Knox and was killed in a bakery two weeks ago.
The Harry Potter character, Marcus Belby, is described in the books as "thin and nervous-looking" and part of Ravenclaw. His Uncle Damocles invented the Wolfsbane Potion, which prevents werewolves from changing during a full moon. The role was Robert Knox's first film appearance.