Jacinda Ardern is set to make her mark in history again, as the first New Zealand Prime Minister to give birth in office - and just the second in the world.
But the baby news was an unexpected surprise for the 37 year old.
Ardern says that after becoming Labour leader in August, she and partner Clarke Gayford had put previous baby plans on hold.
"As it turned out, nature had other plans."
Ardern said the baby was a "fantastic surprise" because the couple had been advised they would need help - fertility treatment - for that to happen.
"I had in the past seen a few people about that but we put an end to all of that when I became the leader," she told the Weekend Herald.
"When I became leader we literally said 'we'll talk about this later.'
"It was just too much… It was just a bit too much to try and make decisions about that so we hadn't made that call actually."
The couple have been swamped with well-wishes after revealing the secret they had held for 99 days, that Ardern is having a baby in June and expects to take six weeks off work.
The couple know the baby's gender but intend to keep it secret.
Marriage has not been discounted but not before the birth, Gayford indicated yesterday. The couple has been together for three and a half years and Gayford will be the primary caregiver after Ardern returns to work.
The baby will take Gayford's surname. Ardern earlier joked in a post to social media that Clarke would be "'first man of fishing' and stay at home dad".
"I think it's fair to say this will be a wee one that a village will raise, but we couldn't be more excited," she wrote.
Ardern's pregnancy revelation – on social media - caps an incredible six months, starting with her taking over the Labour leadership on August 1 when Andrew Little resigned, the election on September 23, being announced as prime minister by New Zealand First leader Winston Peters on October 20 after post-election negotiations, and being sworn in on October 26.
She and Gayford found out she was pregnant on October 13, in the middle of negotiations.
Ardern will be only the second sitting leader, after Pakistan's Benazir Bhutto in 1990, to have given birth in office.
Peters, the Deputy Prime Minister, will take over as Acting Prime Minister during Ardern's absence.
"I have absolutely no qualms, no hesitation and am completely confident that my Deputy Prime Minister will be excellent in the job," Ardern said.
Asked if six weeks was rather a short time to take off, she said she did not want to renege on her undertakings. She was very aware she had taken on the job of Prime Minister.
"So I need to juggle this new role and make sure I do the best I can deal with alongside Clarke.
"But I also cannot renege on the responsibility I have taken on also to lead the country and I am very mindful of that.
"The point is that most parents have to make a judgment call around a parent returning to work and that parent just happens to be me."
Ardern said the morning sickness had stopped but before Christmas but she tried to fight the nausea by snacking.
"I did eat quite a few salt and vinegar chips. I did wonder for a while whether my staff would pick it up because eating chips at my desk quite a bit is not my usual behaviour."
Ardern said she had a small baby-bump showing.
"It's not huge but it's enough for me to be very aware there are certain things I can't wear."
Asked if she avoided a bikini when swimming on the Sunshine Coast in Australia over the holidays, she said she had taken to the water when she had been out for a walk and was wearing a sports bra and shorts.
Ardern's absence from the job will come after the Budget in May, and after the Commonwealth Heads of Government Meeting in London in April where she will meet the Queen for the first time.
The Queen had her youngest two children, Andrew and Edward, after her coronation.
Ardern said she expected Gayford and the baby to travel with her after she first returned to work and wanted to breastfeed for as long as she could.
"I am going to do my best and I think everyone goes in hoping to do their best but knowing things don't always work out as you plan."
International travel in the second half of the year is not confirmed but could include attending leaders' week at the United Nations in September, the Pacific Islands Forum in Nauru, the Apec summit in Papua New Guinea, and the East Asia Summit in Singapore.
The baby news has been widely welcomed across the political spectrum.
New Zealand's first woman Prime Minister, Dame Jenny Shipley, was one of the first to offer congratulations. Helen Clark, Labour's last Prime Minister, said Ardern and Gayford had a "super busy" year ahead.
National leader Bill English, who has six children with wife Mary, said: "A new child will bring real joy to their lives."
Australian Prime Minister Malcolm Turnbull called Ardern and the news has been widely covered across the world.
Peters, whose party has four cabinet ministers compared to Labour's 16, said he was committed to providing good and stable Government in the months ahead.
"Ours is a novel coalition in many respects and the Prime Minister's announcement only reinforces its unique qualities."
Ardern met Peters on Thursday to give him the news and discuss her plans. She had separate talks with Green Party leader and support partner James Shaw.
"That a woman can be the Prime Minister of New Zealand and choose to have a family while in office says a lot about the kind of country we are and that we can be," said Shaw, "modern, progressive, inclusive and equal."
I can't think of a happier start to 2018.
As the news that Prime Minister Jacinda Ardern and her partner Clarke Gayford are expecting their first child exploded on social media yesterday, I couldn't stop smiling — and not just because we had a wonderful story to put on the front page today.
It was because, with one single but utterly significant announcement, Ardern has become an even more inspiring role model for New Zealand women.
As Prime Minister she was already encouraging young women to dream big. Now she has another important message — that women can have a baby and a fulfilling career. Like many women, she chooses to do both. Her partner will be a stay-at-home dad. A thoroughly modern family, and a powerful example.
It is a privilege to be a parent, and the pair will soon discover the life-changing joy that a small person brings. It's not always easy — as working mums and dads everywhere will attest, some days the juggling that goes on would be more at home in a circus tent. But a bad day at the office — hell, even a good day at the office — is always trumped by getting home to a cuddle with your little one.
But that's for the future. Right now, the pair can revel in their historic news. They won't be able to wipe the smiles from their faces.
Congratulations Jacinda and Clarke — we're thrilled for you.
Weekend Herald editor