(CNN) New Zealand's Prime Minister Jacinda Ardern has revealed that she is pregnant, making her the first world leader since 1990 to be expecting a child while in office.

Arden said on Friday that she and her partner, Clarke Gayford, are due to have their first baby in June.

"Clarke and I are really excited that in June our team will expand from two to three, and that we'll be joining the many parents out there who wear two hats," she said in a Facebook post.

"I'll be Prime Minister AND a mum, and Clarke will be 'first man of fishing' and stay-at-home dad."

Speaking to reporters outside her home on Friday morning, Ardern said she would be taking six weeks leave following the baby's birth.

"I am not the first woman to multi-task, I'm not the first woman to work and have a baby, I know these are special circumstances but there will be many women who will have done this well before I have," she said.

Prime Minister Jacinda Ardern and her partner Clarke Gayford speak to the media January 19 in Auckland.

The New Zealand Prime Minister won't be the first leader to have a child while in office. In 1990, then Pakistan Prime Minister Benazir Bhutto became the first serving elected leader to give birth.

Ardern said she learned she was pregnant in October during negotiations to form a minority New Zealand government, "but as many couples do in the early stages, we kept it to ourselves," she said.

During the 2017 election campaign, an interview with Ardern on New Zealand radio went viral and sparked a debate about sexism after a radio host quizzed her on her baby plans just hours into the job.

"I elected to talk about it, it was my choice ... but for other women it is totally unacceptable in 2017 to say a woman should have to answer that question in the workplace," she said.

Reaction on social media was largely positive following the news, with New Zealanders congratulating their prime minister on her announcement.

Morning sickness

When questioned by reporters, Ardern said while she didn't underestimate the challenge of raising a child and running a country, she had a "lot of support" around her.

"And I would say to those people, none of them detected I had pretty bad morning sickness for three months of establishing the government," she said.

The news came as a surprise, she said, as the couple had always hoped to have a child, "but we had been told we would need help for that to happen," she said.

"We wanted a family but weren't sure it would happen for us, which has made this news unexpected but exciting."

Ardern said she asked Deputy Prime Minister Winston Peters to take on the role of acting prime minister for six weeks after the baby is born while she's on parental leave

When questioned by reporters, Ardern said it was "not unusual" for Peters to take up the position of Prime Minister. "He's played that role before, when I go overseas he plays that role," she said.

Congratulations flood in

At 37, Ardern became New Zealand's youngest female Prime Minister in October after the left-wing Labour Party threw its support behind her.

A former DJ and a lapsed Mormon, Ardern is the closest thing New Zealand has had to a rock-star politician in years, attracting mass crowds to rallies and enjoying wall-to-wall press coverage.

Wishing @jacindaardern & @NZClarke all the best as they expect their 1st child in June: a super busy year coming up & much to look forward to. Every #woman should have the choice of combining family & career. https://t.co/Ma6B6OGXJe — Helen Clark (@HelenClarkNZ) January 18, 2018

Ardern took over the Labour Party in August after her predecessor stepped down as the party struggled in the polls. After she became leader of the party, she saw a huge boost in the polls, leading the press to coin the term "Jacindamania."

"Clarke and I are privileged to be in the position where Clarke can stay home to be our primary caregiver. Knowing that so many parents juggle the care of their new babies, we consider ourselves to be very lucky."

Well-wishers congratulated the couple on the news, including former Prime Minister Helen Clark, National Party opposition leader Bill English, Maori Party co-leader Marama Fox and US Ambassador Scott Brown.

"Wishing Jacinda Ardern and Clarke Gayford all the best as they expect their first child in June," Clark said on Twitter. "A super busy year coming up and much to look forward to. Every woman should have the choice of combining family and career."

Warmest congratulations, @jacindaardern & @NZClarke! Everyone at the @NZGreens wishes you all the best for parenthood 👶💚😍 https://t.co/iRrlN1kO3j — Green Party NZ (@NZGreens) January 18, 2018

Ardern and her partner said they already know the gender of the baby, but have decided not to reveal it to the public. "There is very little in our lives now that is a secret or is just for us so we're going to keep it to ourselves," she said.