Studio 10 host shares the moment his little brother vanished without a trace.

Just days away from his 11th birthday in 1987, Studio 10 co-host and journalist Joe Hildebrand watched as his younger brother, nine-year-old Paddy, wandered up ahead on a family bush walk. They never saw him again.

“We were all working along as a group… Paddy just rounded a bend, and we never saw him again,” he told Sarah Harris in an exclusive for the Channel 10 morning show.

For a then 10-year-old Hildebrand, it was hard to grasp that Paddy, who went missing in Lilly Pilly Gully in Victoria and had a developmental delay due to Gastaut syndrome, wouldn't be coming home.

"Even for a couple of days afterwards, I always thought he'd be found. There we so many people looking for him, how could all these people, all these big strong men, how could they not find him?"

Listen: What it's like when a loved one goes missing.

Sharing the details of one of Victoria's largest missing person cases, Hildebrand spoke of how Paddy's disappearance affected his family, already fractured by the breakdown of his parents' relationship.

"I never knew anything different," he said of his brother's profound intellectual disability.

"Once he pointed at the television when it was just on static and said that was what it was like inside his head."

It's been 30 years since Paddy went missing, leaving behind only a yellow hat Hildebrand insists "he would never leave behind". To this day, Hildebrand and his mother visit the site of his disappearance to remember him.

"In a way he’s always there, he’s always in you, he becomes part of you."

Hildebrand's book where he details the incident, An Average Joe, is available for purchase here.

For more information on Australians who are missing, visit the National Missing Persons Coordination Centre.