(CNN) Australia's Deputy Prime Minister Barnaby Joyce has been removed from parliament for being a New Zealander, putting the government's majority at risk.
Joyce was one of five lawmakers ruled ineligible Friday by the High Court in Canberra, but the only one from the lower house.
The Australian constitution bars citizens of foreign countries from serving in parliament. Joyce claimed he wasn't aware he held New Zealand citizenship and has since renounced it.
Joyce previously made headlines worldwide when he threatened to euthanize the dogs of actor Johnny Depp after they were brought into Australia illegally.
The deputy prime minister's removal sparks a by-election, to be held on December 2, endangering Prime Minister Malcolm Turnbull's one-seat parliamentary majority and putting it at risk of an opposition-led vote of no confidence, which could spark a general election.
"It's a pretty simple story, we're off to a by-election (and) I put myself forward to the people of New England as a candidate," Joyce told reporters in his constituency, a rural part of eastern Australia, north of Sydney.
"I had no reason to believe I was a citizen of any other country but Australia."
Speaking Friday, Turnbull said it was "clearly not the outcome we were hoping for" but denied that his government faces any instability in the absence of Joyce.
"We have the support of a majority of members," Turnbull said. A no-confidence vote would require all independent and crossbench lawmakers to turn against the government.
That this turn of events was caused by New Zealand makes it sting even more for the Australian government, which previously accused its closest rival of "conspiracy" against it.
In August, Turnbull accused the then opposition New Zealand Labour Party of working with its Australian counterparts to "undermine the position of the deputy prime minister and the government of Australia."
Labour is now in power in New Zealand following a tightly-fought general election which ended in Labour leader Jacinda Ardern forming a minority coalition government.
Members of Australia's national parliament can't be citizens of another country, according to section 44 of the country's constitution.
It's an archaic law, especially now that a quarter of Australia's population was born overseas and another quarter have parents who were born overseas.
Four senators -- Malcolm Roberts, Fiona Nash, Larissa Waters and Scott Ludlam -- were also deemed ineligible by the High Court Friday. Because of the way members of the upper house are chosen, replacing them will not require by-elections.
Waters and Ludlam, both senators for the Green Party, resigned earlier this year after they became aware of the citizenship issue.
In Joyce's case, his father was a New Zealander, which according to a New Zealand government website, means he is "a New Zealand citizen by descent."
In July, two senators in the Australian Greens stepped down from their positions after discovering they were a New Zealand and a Canadian citizen respectively.
Later the same month, government minister Matt Canavan resigned from his position, but not from the Senate, after he discovered he was an Italian citizen, something he blamed on his mother.
Following the court's decision Friday, Turnbull said his government will refer the matter to electoral authorities, to consider "whether any changes to section 44 should be recommended" or how election laws could be changed.
Turnbull said he wanted to ensure "in our multicultural society that all Australians are able confidently to stand and serve in our parliament."
Joyce has been deputy prime minister since February 2016 when he was elected head of the National party, the junior partner in Australia's governing coalition.
He's also the nemesis of actor Johnny Depp, whose dogs, Pistol and Boo, Joyce threatened to euthanize in April 2016 after they were brought illegally into Australia.
Depp and his then-girlfriend Amber Heard made a famously awkward apology video at the request of the Australian government, in which they said "protecting Australia is important."
Joyce told lawmakers in August he had discovered he was a New Zealand citizen, throwing his position in parliament into jeopardy.