"Come down here, you've got to see this," she says, leading us along a winding path past a flowing garden bed of fragrant lemon balm. Concealed behind the house and its rambling herb garden, a grove of elm trees not visible from the road emerges.

"It's the only property I know of in the village with its own forest, it's a rare gem," she says, her two blue heelers, Scrabble and Zeppy, winding their way happily around her feet as shards of sunlight break through the canopy.

But this is not the Gundaroo home she has lived in and cherished for 40 years. Nor does the tranquil setting reveal the full story of the storm that ripped through her life just a few short months ago.

In late July, at the age of 72, Robyn Thorne said goodbye to her family, boarded a plane for Thailand, and checked into a clinic in Bangkok. A few days later she said another farewell – to her life as a man.

After decades of fighting to suppress a deep and gnawing truth, Peter Thorne – engineer, inventor, loving father and husband – became Robyn.

While not the oldest person to undergo gender reassignment surgery, finding a doctor willing to perform the operation was not easy. The first Thai surgeon she approached refused to perform the operation on anyone over 65, while the second was convinced to go ahead only because Robyn was able to prove her good physical health. Stringent psychological testing also had to be passed before the OK to proceed was given.

"It was the most amazing experience of my life, the nurses and the surgeon were incredible. Finally, I was acknowledging who I really was, and I had to do it, I had simply reached a point where I had no choice but to act."

But having thrown herself into research before the trip, she also knew her decision would exact a devastating toll on her life, the fallout from which was only just beginning.

"It's been extremely hard, I still wake up most nights now and agonise about it, because of what I've done to my wife in particular – I've basically ripped all we had built together out from under her, and at the age of 70. The thing I wrestle with the most is the injustice I've caused my family, that's how they see it and I don't blame them for it."

While the physical transformation is relatively new, the transition to becoming a woman began much earlier.

"It's gone on most of my life, it's gone on most of my married life, to the point where most of my friends and family really knew nothing at all.

"For years I would do anything I could to make my body conform as closely to female as possible that wouldn't be immediately obvious, waxing my legs, electrolysis of chest hair and so on. I had to get special deck shoes for the boat because I wanted to paint my toenails but couldn't wear thongs without being noticed."

It was also more than 20 years ago that Robyn first raised the courage to tell her wife about her inner feelings. Life continued more or less the same for a while, but every time the subject came up – such as Robyn's decision to start taking female hormones or to attend transgender support groups – the constantly suppressed pain would blister to the surface, until the point where Robyn felt she had no choice but to move out of the family home and begin renting a cottage nearby.

"It actually does destroy your life. It's like a tornado that levels everything you've ever done, everything you ever were, and you've got to start again. And in that mess is your family, lying in tatters. I wouldn't wish that on anybody."

Informing her 42-year-old son and 39-year-old daughter of her decision to become a woman had also put an incredible strain on those relationships, despite their attempts to be as supportive as possible.

"I knew that once I did that it was one way, there was no way of putting the genie back in the bottle."

Peter Thorne grew up in Melbourne's inner suburbs, with a happy childhood in a loving family. With his sister they would build billy carts and race them down the hill from the top of the dead-end street they lived in.

It was not until the age of 13 that feelings began to emerge that there was something different, something not right.

"But when you go to an all-male boarding school you push it aside, pretend it's not there and get on with being a bloke."

As the years progressed, those inner doubts continued to grow but there was little help or reference material to turn to in post-war suburban Australia and little opportunity to explore those feelings.

"I had no idea what was going on, I didn't know why it was there, there was no literature available at the time, there was no internet to look it up on."

Feeling confused and alone, Robyn became good at concealing her secret but the strain grew, leading to bouts of depression, poor self-esteem and under-achievement she now recognises as direct results of her attempt to blend in as a normal man. The tough exterior and thick beard that lasted for 17 years became a mask, an attempt to deny an unstoppable change.

"I would buy clothes and be the opposite sex for times, then purge all that, throw them out and think, 'no, this is no good I shouldn't be doing this,' and then you come back to it after a while."

A wardrobe in a side room with a secret latching mechanism in the top became a place to hide female clothes from her family for times when Peter needed to be Robyn, until the day her son nearly discovered the stash. Fortune intervened and he was unable to open the nail at the top of the wardrobe keeping it locked.

"For years I would hesitate to go out in public, then I would just jump in the car and go into town and walk around Civic as Robyn because I was desperate.

"People find it incomprehensible that an apparently blokey bloke would do this – 'why would you want to be a woman?' I'd like people to understand that you are transgender, you don't choose to be transgender, it's involuntary, it bubbles away sometimes for a long time until it becomes something you can't ignore."

Despite the devastation and years of depression, and despite the pain and risk of losing those most dear, the decision to start a new life has brought with it a sense of contentment.

"It's illogical when you think about it, I find it illogical at times but I had to do it. I feel good, and it makes me happy and it makes me complete.

"At my age if I didn't do something now to redress that side of my life it would have been too late. I was already over the age limit for the surgery but because I'm fairly fit I was able to do it.

"I know that I'll never pass as a genetic female, at my age it's too late for that, I just have to work on it the best I can. It's an endless process for me because I started so late, maybe it never ends for anyone."

She hopes telling her story may help those struggling to reconcile their own inner conflicts.

" I felt terribly alone for a long time through this and I had to hide it and feel shameful. In years to come I hope gender will be something that is not terribly relevant, we're all somewhere on the spectrum but at the moment there's still a long way to go.

"I've given my life to my family and I've done all sorts of things with them and for them with great love, but I feel now I need this time to be who I am. I don't regret what I've done."