Imagine you are a senior Army officer, a political operator and a cricket writer moving in circles that are tough, uncompromising and marked by machismo.

Now imagine you have spent three decades moving in these circles all the while battling the inner belief, consciously and subconsciously, that you are a woman born into a man’s body. A belief which, in your 50s, you finally acknowledge, prompting you to make the transition from being a man to being a woman.

That's Cate McGregor’s story. It's one of pain, anguish and despair which eventually gives rise to remarkable courage and ultimately contentment and joy.

"I just felt conflicted. It was like the out-of-tune orchestra. It's like something screeching, that's not right. I just felt excruciating pain," she says.

"We all have to find us. That day comes for every human being. We all wear masks, you know. At some point you have to rip it off and say: 'Who am I?'"

One constant through much of her journey has been Cate's friend, the Chief of Army, David Morrison. As Malcolm McGregor, Cate served with Lieutenant General Morrison in the infantry when they were both young men.

Malcolm left the army for a period, working in politics and as a political writer, before returning to the fold and ultimately becoming Lieutenant General Morrison's speechwriter.

The Army chief speaks in awed tones of his friend's transition.

"I don’t think I can give true lustre to... the courage she's had to show and the journey that she's still got to take to be at peace with herself," he says.

But Cate says she was wrong to fight her inner feelings for so many years.

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"To me, that's the core of the human journey... The front we put on to be prestigious, to be rich, to be all the things we think we have to be when all we have to be is ourselves," she says.

"My journey to that was painful, reluctant and I dragged my heels every inch of the way and, when I got there, all the imagined terrors evaporated."

Military in her blood

Malcolm McGregor was born into a military family in Toowoomba, in regional Queensland. His grandfather, also named Malcolm, fought in the Great War and his father served in World War II.

Sister Mary Saunders says when they were young her brother Malcolm seemed to have the Midas touch.

"Malcolm excelled in the humanity subjects, sports as well. Malcolm was the captain of the cricket team," she says.

Blond-haired, blue-eyed and athletic, Malcolm looked every bit the archetypal boy. But he was wearing a mask.

"The year after my dad died [when Malcolm was eight], I tried on some of my mother’s clothes... She found out that had happened and she was very, very upset about it. I learnt it was a bad idea," Cate says.

"I had disquiet but I got on with my life. I functioned as a boy."

Soon enough, Malcolm decided to follow in the footsteps of his father and grandfather.

"From my earliest conscious memory I knew I wanted to be a soldier," Cate says.

So Malcolm McGregor packed up and travelled south to Duntroon, the Army’s elite training school.

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"I was slight, shy and the place hit me like a tsunami... it was a brutal place."

But over time he became accustomed to the culture. He was focussed on becoming a "warrior".

"I chose to go to the Infantry as the ultimate challenge," Cate says. It was here the young Malcolm McGregor met the man with whom he would forge an unbreakable mateship – David Morrison.

Lieutenant General Morrison remembers the young Malcolm as a brilliant, but somewhat flawed character.

"He was ferociously intelligent. He could be such a serious, talented young officer and at the same time... he had a capacity for errant behaviour, fuelled by both exuberance and perhaps an overindulgence of the grape," he says.

Cate says her younger self was "crazy brave".

"I would do all kinds of mad stuff. I'd get into fist fights at pubs in town. I would fight the biggest guy in the bar."

In the 80s Malcolm left the army and worked for a period in politics, serving first the Labor Party in New South Wales and then the federal Liberal Party.

After the terrorism attacks in September 2001 he returned to the army. By 2011 he was back in league with Lieutenant General Morrison.

Life was good. Malcolm had met and married the woman Cate still describes as her soulmate and the love of her life. "Life really developed a lovely rhythm."

'I was in dire straits'

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Cate says working with her old friend was going brilliantly - for a while. "We were on fire as a team. We were going really well and then my gender thing explodes. And I was in dire straits."

She says feelings she had long suppressed came to the surface.

"I had a feeling that I was meant to be a woman. Conflicting with that was the grinding, crushing reality that I was a 55-year-old male," she says.

"The pain of my last summer as a male is beyond description. It’s a blur."

Eventually, Malcolm had to tell "the chief" what was going on. The anguish he faced was affecting his work.

"We were heading down to Melbourne," Lieutenant General Morrison says. "Mal was sitting next to me on the plane... and Mal said, apropos of nothing, 'what do you think of the whole issue around transgendered people?'"

Lieutenant General Morrison asked, "Is this going where I think it’s going?" And Malcolm replied: "Yeah."

"I didn’t have any experience, I didn’t have any background, I didn’t know what to say other than to keep a conversation going," Lieutenant General Morrison says.

Later, as they left the function, Lieutenant General Morrison took his mate by the elbow.

"I’ll remember it until the day I die. I can remember just saying: ‘I’m with you.’

"I don’t know what is happening in your life, I can’t empathise with you on that point, but I can assure you that you are my mate and I will stay absolutely rock solid with you."

Shortly after Cate had made the transition to becoming a woman Lieutenant General Morrison wanted to meet her.

She warned her friend and boss she looked very different. But he wanted to see her, to make sure she was okay.

"Within 20 seconds we were laughing in a way that I had always been able to do with Malcolm," Lieutenant General Morrison says. He says Cate is the same person as Malcolm, but living a different life.

Lieutenant General Morrison wasn't the only mate who stood by Cate.

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Pollster Mark Textor, a friend from Cate's days working for the Liberal Party during the leadership of John Hewson, says his friend was never quite content. Mr Textor says that's all changed.

"The way I see it personally is the same person expressing herself in a different way - but expressing parts of herself that she’s never expressed before because she’s happy,” Mr Textor says.

As for Cate herself, while she says some people have responded to her journey negatively, most have been gracious. And she is herself truly content, perhaps for the first time in her life.

"It’s almost too exquisite being alive, I really mean that. It’s a wonderful feeling to be alive and be me."

Watch Australian Story: Call Me Cate on Monday at 8pm on ABC1 or catch-up on iView.