Why has Leo Varadkar suddenly resigned as Irish prime minister?

Leo Varadkar’s decision to step down as prime minister of Ireland was so surprising that, according to reports, not even colleagues from his centre-right party, Fine Gael, saw it coming.

The Republic of Ireland’s taoiseach (the Irish Gaelic word for “chief” or “leader”), who will resign his post as prime minister as soon as a successor is chosen by his party and then approved by the Irish parliament, cut an emotional figure as he made his announcement on the steps of government…