Rob Knox (r) was trying to protect his brother, the court heard
The man accused of stabbing Harry Potter actor Rob Knox to death had earlier waved a knife in the face of one of his friends, a court has heard.
Callum Turner, 19, testified that the accused, Karl Bishop, had stuck his hand through his open car window and waved a knife very close to his face.
Mr Bishop denies murder in the fight with Mr Knox outside a bar in Sidcup, south-east London in May 2008.
Mr Turner said he tried to intervene when he saw Mr Bishop threaten others.
Mr Bishop, 21, from Sidcup, denies murdering the teenage actor from Swanley in Kent and five charges of wounding, saying he was acting in self-defence.
A long-time friend of Mr Knox and his younger brother Jamie, Mr Turner broke down in tears describing the last moments of his friend's life to a jury at the Old Bailey.
Mr Turner told the court that before the stabbing he had been in a car outside a nearby Tesco Express when he saw Mr Bishop pointing knives at Jamie and another friend.
He said he then drove up on the pavement beeping his horn and flashing his lights to "disperse" them.
"The defendant ran up to the window. He was shouting very loudly 'Come on big man, get out of the car'."
He said that Bishop then put one of his knives through the open car window about a hand's distance from his face.
"I have never ever felt so scared in my life," Mr Turner said. "I was begging him to leave me alone, I was begging him not to hurt me."
The scuffle happened just moments before Mr Bishop was tackled by Mr Knox, who the court has heard was attempting to disarm the man in order to protect his younger brother.
Mr Turner said he joined in the melee to restrain Mr Bishop and then realised his friend was seriously wounded.
"I was there at that time as well, trying to restrain the defendant, then turned around to see Rob just staring, blank-faced."
The trial continues.