Riana Tromp speaks for the first time about her family's baffling road trip.

Riana Tromp has described for the first time what led to her family making headlines when they went missing last year.

On Monday 29 August 2016, parents Mark Tromp, 51, and wife Jacoba, 53, and their adult children Riana, 29, Mitchell, 25, and Ella, 22, left their farm with little warning on a strange road trip.

The family fled their Silvan berry farm, east of Melbourne, without mobile phones or credit cards and drove 800km north to Bathurst where father Mark was separated from the family.

On Tuesday morning, as the family made their way to the Jenolan Caves the remaining members started to leave the road trip. Mitchell left at Kelso and later sisters Riana and Ella separated.

Ella was reported to have stolen a car and drove south to the town of Goulburn.

Mark Tromp was found wandering along on road in Wangaratta and wife Jacoba was found in Yass wandering the streets.

Ms Tromp was found in a "catatonic state" and did not know her name or where she was.

Riana Tromp told Women's Day her father was suffering from a mental breakdown and he thought the family was in danger.

In the interview, she said the incident was "very scary" and she started believing she was in danger.

"You do start thinking the same," she said - although her father had never done anything like that before.

The 30-year-old told the magazine she believed her father had a build-up of stress that caused the incident.

Listen: Another case that baffled Australia, on Mamamia's True Crime podcast. (Post continues after audio.)

"You have a few things and they do build up - you can get sick in some way," she said.

Although things are said to be getting back to normal now, Ms Tromp says the family were "all very embarrassed".

“We didn’t want to be famous, that’s for famous people,” she said.