Australian senator Nick Xenophon will refer himself to the High Court, after he discovering he's a British overseas citizen.
Xenophon is a citizen by descent, after his father came to Australia in 1951 from Cyprus, which was then a British territory.
"The circumstances of this are bizarre and rare," he told reporters.
He said he never contemplated the possibility he might be an overseas citizen.
"I never contemplated that I could have been a British colonial citizen, and that is why I didn't go through an act of renunciation with the UK," he said.
"It seems that being born in Australia, according to 1948 UK legislation, makes me a colonial Pom - something that has stunned me and my 86-year-old father."
He is the latest senator to be caught up under section 44 of the constitution, which bans dual nationals from serving in the senate.
Matt Canavan, Larissa Waters, Scott Ludlam, Malcolm Roberts and deputy prime minister Barnaby Joyce have all been referred to the court to determine whether they will be disqualified.