Rudi Boa, 28, was killed as he tried to protect his girlfriend from a drunken attack by another British traveller in a remote Australian holiday camp.
Mr Boa's aunt, Marie Chisholm, from North Kessock, Inverness, said she believed the incident at the Blowering Holiday Park, in the town of Tumut, New South Wales, was related to an earlier row about religion.
The couple were staying on the site, along with Alexander York, a backpacker from Essex who has been charged with Mr Boa's murder.
Ms Chisholm said: "They had gone for a pint after work, then back to the camp site. I think they had been having a discussion about religion. Whether the guy had taken umbrage about it I don't know, but Gill had decided that they should get back to the site.
"When they got back, Rudi was in the tent and Gill was outside when the guy came up and tried to strangle her. Rudi rushed out to save Gill and got stabbed."
The mother of Gillian Brown, 29, who is understood to have witnessed the stabbing of her boyfriend, said her daughter had been left "devastated" by the murder.
Miss Brown has been treated for shock at a local hospital following the incident.
Yesterday her mother, Jenny Brown, speaking at the family home in Nairn, said the couple met five years ago while they were both studying biomedical sciences at Edinburgh's Napier University, and had taken a year off from their jobs to travel to Asia and Australia.
"Gillian couldn't have asked for a nicer guy," said Mrs Brown. "Rudi had lots of friends. He loved the outdoors and they were a lovely couple. She's devastated."