Prime Minister Jacinda Ardern says she broke news of her pregnancy to deputy Winston Peters over a few sandwiches and a cup of tea at his home.
Jacinda Ardern will take six weeks off after the baby is born in June and Mr Peters will step up to cover her duties during this period.
Ms Ardern said she told Mr Peters the news in person.
"I went round to his home and we had a chat over a few sandwiches and a cup of tea and he's been fantastically supportive. We talked - basically around the logistics - as well as him sharing his congratulations."
People had made assumptions about Mr Peters and any ambitions he might have to be prime minister, she said.
"My view is that based on what I've seen of the time we've worked together - his goals are mostly about what he can achieve for people rather than his own personal position.
"When you think about it, taking on the job for six weeks, having to stand up in Question Time on my behalf and do all those parts of the job, there's not a lot of glory in that so I'm grateful more than anything," she said.
Ms Ardern said she had felt overwhelmed by the messages of support.
"I know that there are people who are critical, who haven't necessarily welcomed this news and look I understand that.
"Had my late grandmother been around, she might have been one of them."
She was more worried about the future privacy of her child.
"That is something that Clarke and I have talked about a lot because of course I've chosen to work in this arena and kids don't. I'm not the first to struggle with this dilemma.
"Over time I think we will probably try and establish some boundaries but at the same time - we are public and our lives are public. We'll just try to find that balance."