Jacinda Ardern's burnout highlights the pressure world leaders face - BBC

She says Ms Ardern appeared to have a "very, very demanding programme" - plus an extra layer of pressure from "balancing a family and career" at a time of major political challenges.

Ms Clark believes that while the pressure on leaders has "always been immense" it has become even more so "in the era of social media and the 24-hour news cycle and click bait and trolling and conspiracy theorists and the rest of it".

It is more common for leaders to be forced out than to admit they have burnt out, but there are several examples of political figures publicly struggling with the demands of recent years.

Political biographer Sir Anthony, whose work has chronicled the lives of numerous British leaders, says many prime ministers finish their time in office exhausted.

Ms Ardern said she was looking forward to spending more time with her family - being there when her daughter starts school and "finally" marrying her fiancé, Clarke Gayford.

For people hoping for a future life in political leadership, Ms Clark warns that the top job is "a lot of grind" and requires a belief "that it is worth the time and effort and long hours and that you can really achieve things".