Many people living, voting and paying tax in Australia may have technically been stripped of their citizenship and not even realise it.
It's because of the now-repealed section 17 of the 1948 Citizenship Act.
Between 1948 and April 4, 2002, Australian adults who got a second citizenship automatically lost their Australian citizenship.
And between November 1984 and April 2002, they didn't even have to be outside Australia when they took up their second citizenship to trigger the loss of their Australian rights.
That was the case for Matthew Niall, who had his Australian passport cancelled last year because he became an Irish citizen more than two decades ago.
His case has highlighted the plight of those caught in legal limbo, with experts saying it shows the "dysfunction" of our citizenship legislation.
So how did we get here, when can citizenship be stripped under the law, and what are some solutions?
Why was the law changed?
On April 4, 2002, the federal government repealed the law, saying at the time the change was needed to keep in step with a new globalised world.
Up to 700 Australians had been losing their citizenship each year.
Philip Ruddock, who was the immigration minister under the Liberal government, told the ABC he spearheaded the move to have section 17 repealed.
"The reason for the change was that there were people making representations to government," he said, especially those who had returned to the UK and wanted the opportunity to take up British citizenship and travel more freely in Europe.
But Mr Ruddock said making the legal change apply retrospectively wasn't something his government considered at the time.
"I hadn't contemplated giving those who had forsaken their nationality the opportunity to resume it, and I've had no representations at any time since that change was made for that to occur," he said.
To do so, he suggested, would be to "impose" Australian citizenship on people who "may have wanted to renounce it deliberately".
The repeal also remedied an inconsistency in the law.
Between 1984 and 2002, a foreign-born person could take up Australian citizenship and keep their first nationality — if their country of origin allowed it — making them dual citizens.
But Australian-born people could not take up a second citizenship and keep their Australian citizenship.
Ignorance of the law 'no excuse'
Mr Ruddock said at the time, the law operated as intended, and ignorance of the legislation was "no excuse".
"You can't speed on a road and say, 'Oh, I didn't know, I was ignorant. I didn't know this was a speed limit on this road'."
He said it was normally up to foreign governments to tell Australia if an Australian had been granted citizenship.
In Mr Niall's case, "the approach that I would take is to encourage the young person involved, to seek to engage with the present government, with a view to ascertaining whether they can have their citizenship restored," Mr Ruddock said.
Law 'not at all clear'
Migration lawyer Karyn Anderson said she received a couple of clients each year who had lost their citizenship due to section 17 — and it can impact them in substantial ways.
She said it could become a "bureaucratic nightmare", especially when trying to get citizenship for children — something that could be more complicated once they are over 18.
"I've had clients who've been voting in elections, have been using Australian passports," she said.
"It wasn't at all clear."
She said each foreign process was different, and it was not always someone's "sole and dominant purpose" to acquire a second citizenship.
She referenced "oleh status", where Israeli citizenship is bestowed on permanent residents, from which they must opt out.
She also mentioned Italian-born Australians who returned to Italy and automatically acquired Italian citizenship.
So what happens if I lost my citizenship without knowing? Do I need a visa?
The current Immigration Minister Andrew Giles said in a letter that lost citizenships might never come to light.
For those who are overseas, their passport is cancelled and they are forced to rely on their second citizenship.
For those who are on Australian shores when their citizenship ends, they are granted an "ex-citizen" visa automatically under the law.
That is a permanent visa that allows the person to live here, but it ends the moment the person departs the country.
To re-enter, they would have to apply for another visa.
Can I get my citizenship back?
People who lost their citizenship while in Australia are advised they can apply to resume it and become an Australian citizen again.
It costs $210 and the person must satisfy the Department of Home Affairs that they are of "good character".
Ms Anderson said while there was a pathway to resume citizenship, "it is certainly possible for it to be refused — it's not a rubber stamp".
If someone had close connections to Australia and spent their formative years here, she questioned whether it was appropriate to refuse them on character grounds.
She also said applications could be refused not just for criminal convictions, but also for failing to answer questions correctly on a form.
"Afghan clients who often don't have a naming tradition, who don't have a clear surname and first name, who adopt a name, because they're required to because of our processes, are then met with all sorts of difficulties when they apply for citizenship," she said.
"So it's not only identity issues, but also character issues. Did they do that on purpose to help a family member come out from a war zone?"
What about stripping people of citizenship due to alleged terrorism?
Citizenship debacles have made headlines in recent years – from the dual citizenship fracas that engulfed many elected members of parliament, to legal grey areas and attempts to deport Indigenous non-citizens.
The former government's steps to strip dual nationals suspected of terrorism offences of their Australian citizenships has triggered a wave of legal opinions.
Last year, a man suspected of joining Islamic State, Delil Alexander, won a High Court challenge against the government's decision to revoke his citizenship.
In that case, the High Court ruled the stripping of someone's citizenship was so serious it should only be handled by a judge, and the home affairs minister could not take it away.
Dr Sangeetha Pillai, a constitutional lawyer at the Kaldor Centre for International Refugee Law, wrote the High Court's finding meant that section of the law, section 36B, was invalid.
"This means that anybody who was stripped of their citizenship under that provision is an Australian citizen again," she wrote for Australian Public Law.
The government said 22 people had been stripped of their citizenship over alleged terrorism, but only two lost citizenship under section 36B.
'An extremely serious matter'
Prior to this court case, back in 2019 the Australian Human Rights Law Commission wrote in a submission on citizenship losses due to terrorism that "involuntarily removal of citizenship is an extremely serious matter".
"Roman law, for example, referred to this action as civiliter mortuus or 'civil death' for the affected person.
"Errors in the application of these provisions could mean that a person's right to enter and remain in their own country, Australia, are seriously and arbitrarily impaired, having adverse consequences for numerous other human rights."
Mr Niall said when he told people he had lost his citizenship he was met with disbelief or worse — a suspicion he had done something terrible to warrant his citizenship being taken away.
Legal scholar Kim Rubenstein, a professor at the University of Canberra who has been consulted on citizenship law, said because of the amount of attention there has been surrounding citizenship and terrorism, the public may draw inaccurate parallels.
"I think that there would be an understanding through the community that this is an unfair association between terrorist activity and someone's changed dual citizenship," she said.
She added one of the grounds for the High Court ruling was that the stripping of citizenship was punitive, even if that was not the intention of the legislation.
Case highlights systemic issues
Sanmati Verma, managing lawyer at the Human Rights Law Centre, said Mr Niall's case prompted further questions.
"This is an unfortunate case of an administrative oversight, which has meant that a former citizen was not advised of his altered legal status for 20 years and treated for all intents and purposes as an Australian citizen," she said.
"While there is a 'fix' in this case, in the form of a further citizenship application, there are bigger questions to be asked about the way that applications are processed and decisions are made within the citizenship section of the Department of Home Affairs.
"This is just one example of the dysfunction that characterises citizenship-related processes — people are waiting for record periods for their citizenship applications to be processed, and the department often demands impossible evidence of identity and former residence, even from people who have lived in the Australian community for decades and have no connection with the country in which they were born."
What are some solutions?
Ms Anderson said there could be a question written into passport forms, asking an applicant if they had taken out another citizenship.
"There would be ways of ensuring that every time an Australian applies for a new passport, they're asked that question, and it doesn't take decades for the department to work out," she said.
Professor Rubenstein has also suggested there could be a way for parliament to make a legislative fix, and re-instate citizenships as if they had never been lost.
"I think the spirit that any government should be taking in thinking about citizenship law should be one about inclusion," she said.
She said when a person who had lived their whole life as an Australian was suddenly told they were not a citizen, it could be seen as an injustice and didn't sit well with the broader community's understanding of citizenship.
Professor Rubenstein added an inclusive approach to citizenship law was needed for a cohesive and egalitarian society.
"If you think of citizenship like marriage, then of course we have a commitment to monogamy and you only have one partner," she said.
"But if you think of citizenship like parenting, then when you're a parent, and you … have a second child, no-one ever questions that you are in some way diminishing your relationship with your first child."
Editor's note: A previous version of this story stated that Australian adults who acquired a second passport between 1948 and 2002 automatically lost their citizenship. The article has been corrected to clarify it was the acquisition of a second citizenship, not a passport alone, that triggered the forfeiture of Australian citizenship.
The article has also been updated to clarify that between 1948 and 1984, section 17 referred to Australian adults who acquired a second citizenship while outside Australia. In November 1984, it was amended to remove the requirement to be outside of Australia.
