Steve Irwin started his working day at 2am due to “terrible insomnia”.

The late Crocodile Hunter star – who died aged 44 in 2006 after being pierced by a stingray barb in the Great Barrier Reef – struggled with the sleep disorder, according to his daughter Bindi, 26.

Appearing on Sarah Grynberg’s A Life of Greatness podcast, she said: “He had terrible insomnia. I mean, he just never slept.”

According to the Australasian Sleep Association, insomnia is seen in people who have difficulty falling asleep or maintaining sleep, and waking up too early at least three nights a week.

Steve had Bindi and her brother Robert, 21, with his wife Terri.

Bindi, who was just eight years old when her father died, and her family were “going through some of his things” as they cleaned out a cupboard in an office to prepare for a renovation at Australia Zoo.

They found a lot of his scientific research “hidden in the back of the cupboards”, which reminded her of Irwin’s sleeping habits and work ethic.

She said: “We were going through his cupboards. And people may not realise that he had such a scientific mind.

“I was looking through his journals and he would just write down, I mean, thousands, it’s not an exaggeration, but thousands of pages worth of information and facts and studies and findings.

“Dad would wake up at 2am in the morning. I swear to you, his day would start at 2am. And by the time everyone else’s workday has started, he’d put in a full day’s work.”

Bindi explained that her late dad preferred “researching and studying” before dawn, when “the world is dark” and he had peace and quiet.

She insisted his efforts helped Australia Zoo have the world’s largest study of crocodilians, as he delved into “every facet of the information that people shared with him”.

And while most of her dad’s fans saw him as a “passionate, wild human being” on television, she hopes people recognise all sides of him.

She added: “I really wish people could have also seen his scientific mind, which was second to none.”