Speaking at a press conference in Sydney, Connie Casey told how Mr Hagland was repeatedly punched and kicked in an apparently motiveless attack in the early hours of Saturday morning.
"He didn't know these people. They just picked him off the street, and they killed him," she said. "He died really quickly. He didn't stand a chance - this man was like a robot."
Mr Hagland, 28, and Ms Casey, 25, of West Hampstead, London, were walking along a brightly-lit street yards from Bondi beach when they were accosted by two men in their mid-twenties thought to be high on drugs.
One man knocked Mr Hagland to the ground and repeatedly punched and kicked him until he collapsed unconscious on the street. He was taken to St Vincent's Hospital in the city where he later died of head wounds and internal injuries.
Ms Casey said she and Mr Hagland, who is the cousin of EastEnders star Sid Owen, who plays Ricky Butcher, were on their way home after attending her leaving party at the Australian Trade Commission.
"These men were coming towards us and I just knew by the look on this man's face he was dangerous and was going to do something," she said.
"I said to Brian 'don't say anything to him'. I was given a presentation of flowers from work and he was holding the flowers and holding my hand. He said 'I'm not going to do anything.'
"Then this man just ran up to him straight away and he said 'come on, come on, let's have him'. And his friends stood back and he just punched Brian and dragged him to the ground. He was on top of him and I hit him with my bag, and was hitting and hitting him because my bag was quite heavy."
Ms Casey said she went to get help and call the police. "When I came back he was unconscious and he was covered in blood. It happened in minutes."
She said the attacker's eyes were "glazed. He was robotic. He looked as if he didn't even see Brian".
Mr Hagland and Ms Casey had planned to get engaged in Tahiti later this year before returning to Britain in January 1997 when Mr Hagland was set to return to work as a driver for the Post Office.
The attack was the second time Ms Casey had been confronted by violence recently. Last year she was the victim of a hold-up at a north London jeweller's shop when the robbers dowsed her in petrol and threatened to burn her alive. She used the compensation money received after the robbery to pay for her trip to Sydney, which was supposed to help her to recuperate.
Yesterday, the dead man's uncle, Ron Hagland, said that his nephew was "a gentle giant" who would have gone out of his way to avoid a fight. "He was a model son," he said, "Brian would go mad if he saw anybody killing a spider. He was an absolute diamond, a really clean-living bloke with no problems whatsoever."
Last night, a spokeswoman for the Sydney police department said that there was a possibility that Mr Hagland's attacker may be injured due to a trail of blood leading from the scene along Bondi beach.
"We have followed a trail of blood and think that one of the offenders could be seriously injured," the spokeswoman said.
Mr Hagland is the second Briton to be killed in the Bondi beach area of Sydney this year. Last April a backpacker, Gawen Whalley, 22, of Dorset, was stabbed to death by a gang of youths as he walked to his temporary home on a neighbouring beach. It is thought by Australian police that both he and Mr Hagland could be the victims of a wave of motiveless "thrill-seeking" killings that are sweeping the area.Reuse content