U.K. Prime Minister Theresa May Welcomes Ireland's Prime Minister Leo Varadkar [Getty Images]

Leo Varadkar, Ireland's prime minister, left, speaks as Theresa May, U.K. prime minister, looks on during a joint news conference inside number 10 Downing Street in London, U.K., on Monday, June 19, 2017. The Republic of Ireland is the Northern Ireland's biggest trading partner outside Britain. Photographer: Simon Dawson/Bloomberg via Getty Images

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