The British government has got it wrong in its legal battle with a Northern Ireland woman over post-Brexit issues of identity and nationality, Leo Varadkar has said.
Emma De Souza won a case against the Home Office after it deemed she was British when her US-born husband applied for a residence card.
The Home Office has appealed.
The taoiseach (Irish PM) said the Good Friday Agreement allows people to be British, Irish or both.
Ms De Souza's case has thrown a spotlight on how Brexit could have consequences on identity and the rights of British and Irish citizens in Northern Ireland.
The UK had been due to leave the EU on 29 March, but the deadline was pushed back to 31 October after Parliament was unable to agree a way forward.
Anyone born in Northern Ireland has the right to identify as Irish or British or both, thanks to the Good Friday Agreement, signed in April 1998 by the British and Irish governments and Northern Ireland's political parties.
Ms De Souza applied for a residence card for her US-born husband in December 2015, making the application under her Irish passport.
However, the Home Office rejected the application as it deemed Ms De Souza was British, even though she says that she never held a British passport.
They requested that Ms De Souza either reapply as a British citizen or renounce her British citizenship to apply as an Irish citizen.
But she challenged the decision, citing the Good Friday Agreement's terms that assert her ability to identify as Irish, British or both.
Ms De Souza won her appeal, but the Home Office is challenging that decision and the hearing is pending.
She has said previously she fears Brexit could make the outcome even more uncertain.
On Tuesday, while speaking in the Dáil (Irish parliament), Mr Varadkar also said he would be meeting UK Prime Minister Theresa May in Paris on Wednesday and that he expected next week's UK elections to the European Parliament to be very interesting.
He said he believed the third seat in Northern Ireland was "very much up for grabs".
Mr Varadkar added that EU leaders would assess the results in the following week.
This article was originally written on 14 May 2019 and was updated on 1 August 2019 to include more information on the case.