Even as a child, Matty suspected something was not quite as it seemed.

"I can remember looking at family photos and wondering where I got my red hair and freckles from."

Parents Eveline and Tony always seemed to have answers.

But when Matty turned 18, Mum and Dad finally revealed the truth about how their two children Matty and younger sister Beth were conceived.

And Matty has struggled with the legacy of their choices ever since.

When 27-year-old Eveline held newborn Matty in her arms for the first time in 1984, it felt like the most amazing moment of her life.

Her then-husband Tony was infertile, so the Perth-based couple had sought out a doctor to help them conceive using donated sperm.

They both saw it as a chance to create the family they wanted but Catholic-raised Eveline struggled with whether the decision to use the anonymously donated sperm was the right thing to do.

"I was really ambivalent because I very much am not a Catholic, or religious, and wasn't really then, but it still obviously had that bit of a hold in my head," she says.

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Eveline was also worried about the possibility her children might have other siblings from the same biological father out there. And what if they met?

In the early 1980s, using donor sperm for conception was generally kept a secret, says Kate Bourne, a counsellor with the Victorian Assisted Reproductive Treatment Authority (VARTA).

The focus was on protecting the adults involved in the process from things like unwelcome child maintenance or estate claims down the track, and also avoiding the stigma associated with infertility.

"For a man to be diagnosed with male infertility was very, very difficult and emasculating," Kate says.

"We hear stories of couples saying the doctor even said, 'Go home, make love to your wife and we'll never really know who is the genetic father'. So it was very much the way things were done then."

Since 2005, anonymous sperm donation is no longer considered acceptable practice in Australia, but it is still very common in some places.

Back in 1983, Eveline didn't give much thought to the sperm donor's identity or that not knowing it would cause problems for her children later on.

"I just accepted it I didn't need to know."

But that was something she later came to regret.

A couple of years after Matty was born Eveline and Tony had Beth, using sperm from a different anonymous donor.

As their children grew older, Eveline wrestled with when to tell them they were donor conceived, but it never seemed to be the right time.

Matty and sister Beth were both donor conceived, using sperm from different men.

(Supplied: Eveline Durkin)

Matty and sister Beth were both donor conceived, using sperm from different men.

Tony was reluctant to reveal he wasn't Matty's biological father, fearing rejection, and he says he wanted to leave it until the children were old enough to understand.

"I think if you tell a six-year-old or an eight-year-old they might rebel there might be heartache."

It wasn't until Matty was about to leave home to start university that Eveline and Tony called a family meeting to explain their children's origins to them.

Matty remembers that "family chat" well.

"My parents were scared. And I was angry."

Incredibly though, despite having visceral feelings on the inside, Matty didn't show them at the time, having more concern for Eveline and Tony's feelings.

"I told them, 'It's fine. You've always been here for us. And this won't change anything.'"

But things weren't fine.

"I was feeling that anger and betrayal I felt like I'd been deceived for 18 years."

VARTA counsellor Kate runs workshops for donor-conceived people and their families, and understands the effect this kind of experience can have.

"The impact is often about a lack of trust and the impact on your identity," she says.

"You think that you know who you are and then suddenly the foundation stone from that is different so it results in having to sort of review your identity."

Matty was especially upset the sperm donor was anonymous, suggesting that tracking down a biological father would be impossible.

Now 35 years old and living in Hobart, Matty understands why Eveline and Tony were reluctant to disclose, but still finds it hard to deal with.

"Back when I was conceived in '83, parents were often counselled to not disclose because it would make their lives easier It didn't make our lives easier."

One of the hardest things for Matty, who uses the gender-neutral pronoun "they", to reconcile is the way their parents had skirted around the truth.

They remember asking at five or six: "Is Dad my real dad?"

"Yeah, he's your father," came the response, and Matty's red hair was explained away by pointing to other redheads in their extended family or the red tints in Eveline's hair.

Eveline accepts that Matty now sees this as a case of being lied to.

"Even when I asked questions directly, the whole truth hadn't been said. And it took a long time to process that," Matty says.

A recent selfie from Matty.

(Supplied)

A recent selfie from Matty.

Eveline has worked hard to understand Matty's distress, and done what she can to help her children deal with the consequences of finding out they are donor conceived.

Matty's father, now separated from Eveline, is sorry for Matty's struggle, but doesn't see how things could have been done differently.

"I don't regret telling Matty and Beth at that age," he says.

"I don't think we were lying to them. I think we were honest with them and telling them at an appropriate time in their lives."

Traditionally, donor-conceived children and adopted children were thought of differently by health services.

When Matty was born, there was a push to tell adopted children their biological origins while they were still young. It was understood that this was better for their development, sense of identity, and wellbeing in the long-term.

But this approach wasn't applied to donor-conceived children.

"I don't think people really thought about the person conceived from the donation treatment and what their needs might be," Kate says.

But finding out in adulthood that you are donor conceived risks a loss of trust in your parents, and in your own sense of self.

"The recommendation has gone from medical staff encouraging not to tell, to actually encouraging parents to tell," Kate says.

Kate says research suggests it is best to tell children they are donor conceived before puberty.

"It's better to start the conversation while the child is very young so that they can't ever really remember a time where they didn't know."

"This is just part of who they are. And part of their family's story."

It hasn't been an easy road for Matty's family.

Tony had been reluctant to talk about the topic, Matty says.

Five or six years ago Matty's anger forced the issue.

"I said [to Dad] something like 'Dad we're not father and child here, we're something else.' And he said 'What? Like super friends?' And that's when things changed for us.

"We could build a relationship based on the truth."

Matty now feels they can more fully celebrate what they have, and Tony's loving role in Matty's life.

"The special relationship between a father who's brought you up without having a biological connection, and has always been there, is a really special one. And that became a point of pride for my dad."

Tony and baby Matty.

(Supplied: Eveline Durkin)

Matty's relationship with mum Eveline after the revelation has been more open, but in some ways harder.

Despite the relief of sharing the news, Eveline gets very emotional every time she talks about it.

"She's seen the pain and the anguish the decision not to disclose has caused and the separation from kin has caused," Matty says.

Eveline says there is "a lot of guilt and a lot of regret" that it wasn't done differently.

"It's a work in progress for all of us and it probably always will be," she says.

However the family has reached a level of acceptance and peace.

Matty still holds some anger mainly at a society that supported non-disclosure and has placed so much weight on having your own children.

"I think a lot of people believe that if you're unable to have a child of your own, that makes you somehow less than other people. And so those pressures also were part of my parents' decision."

For Matty the cost of secrecy has been clear.

"I've lost 30-odd years of being able to grow, knowing where I've come from and that's not something that I can ever get back."

Kate says she regularly hears of people accidentally discovering they were donor conceived.

"I've had quite a few clients where they've been given [a DNA ancestry] testing kit for Christmas or for a birthday and suddenly they've discovered that their dad isn't their biological father."

"People say they would much rather find out from their mum and dad than from a test."

Matty's sister Beth is now an activist for donor-conceived people in Perth.

(ABC News: Rhiannon Shine)

Matty's sister Beth is now an activist for donor-conceived people in Perth.

Kate stresses it is never too late to share the truth.

"It's about thinking about how to do that in a loving and supportive way."

She runs a seminar that helps families with this process, and VARTA provides resources for donor-conceived people and their families.

"It should be a very proud story to be told and not a dirty little secret."

Around a year ago, after a long and complex process, involving DNA testing and searching on social media, Matty connected with their biological father, Alan.

"We just started sort of talking on Facebook and it was surreal," Matty says.

The first time Matty saw a picture of Alan, the physical resemblance was obvious, and then they found out Alan studied engineering.

A young Matty and family.

(Supplied: Eveline Durkin)

A young Matty and family.

This "put a lot of pieces into place", says Matty, who as a child used to pull their toys apart instead of playing with them.

"We share a sense of humour and we also share a fervour for robust discussion," Matty adds.

But feeling a connection to a stranger was "scary" and raised a whole lot of questions.

"What are we going to talk about? What do I want to know? What do we have in common? Will I be rejected if I approach?"

And amid all this, Matty has been worried that reaching out to their donor might hurt their dad, Tony.

More:

Donor conception and the cost of keeping a secret - Science News - ABC News