Derryn Hinch shock revelation on Who Do You Think You Are?

Derryn Hinch has unravelled a secret that has long haunted his family — the identity of his maternal grandfather and why his grandmother refused to reveal it.

Derryn Hinch’s grandmother took the identity of his mother’s father to her grave. Picture: Supplied

Derryn Hinch has discovered the shocking truth in a mystery that has haunted his family for a century, after a DNA test revealed the identity of his grandfather.

The journalist and former senator said his grandmother’s lifelong refusal to tell his mother who her father was caused much heartache, but he now understood why.

He learned his grandfather was war veteran George Berry, who fathered a child with another woman four months before having a child with Hinch’s grandmother.

The secrets were revealed in Tuesday night’s episode of SBS’s Who Do You Think You Are?

Hinch's maternal grandfather, George Berry.

Hinch's mother, Betty Edlin, and grandmother, Phoebe Edlin.

“It shocked me that my grandfather George Berry fathered another child only four months before my mum was born,” Hinch said.

“I’ll concede I had a flash of resentment and a bit of anger. I thought, ‘how dare you?’

“But then, I don’t have sympathy for what he did, but I have empathy for him because I do believe he had a permanent war injury.”

Hinch’s grandfather – an injured World War I veteran on a war pension – went on to have another four children with the other woman.

It’s unclear when Hinch’s grandfather officially married the other woman, Myrtle, but they never divorced.

George Berry died aged 74 in 1973.

For years Hinch, who grew up in New Zealand, had scolded his grandmother for refusing to tell his mother who her father was.

But he now understands why his grandmother took the secret to her grave.

“I think my mum’s heartache, I guess, all those years was not knowing, never knowing, but I’m starting to understand now why her mother didn’t tell,” Hinch said.

“I think my nanna was trying to protect my mum, and that made my heart warm a lot more towards my grandmother.”

Hinch travelled around New Zealand to uncover his past. Picture: Supplied

Hinch’s late mother, Betty Edlin, was born in Petone in Wellington in 1920.

His grandmother, Phoebe Edlin, later married a man named William Hood, who raised Betty as his own daughter.

Hinch had long theorised his grandfather was an English sailor, because his mother as a child was given a painting of herself in a distinctive map tube made from lead.

Instead, ancestry experts revealed his grandfather was a local man who lived only eight blocks from his grandmother.

While travelling around New Zealand for the ancestry search program, Hinch also learned his grandfather was an infantryman who fought on the frontline in France, including a key battle against the Germans that helped win the war.

Berry’s war records reveal he was “blown up by a shell” in March 1918, and was sent to a hospital to recover, but was back on the frontline three months later.

He was injured again, suffering serious burns, and was eventually discharged from the army for medical reasons. He was granted a war pension and lived to the age of 74.

“I’ve found this journey to be a rollercoaster,” Hinch said.

“It has been taxing, but it’s been wonderfully taxing. It’s torn at the heartstrings.”

Derryn Hinch’s episode of Who Do You Think You Are? is available to stream now on SBS On Demand.