Prime Minister Jacinda Ardern will make a cameo appearance on The Late Show with Stephen Colbert tonight in an episode where he confirms he will visit New Zealand next month.

The appearance was a last-minute addition to Ardern's New York schedule. It was filmed today and will be aired tonight.

In the segment, Colbert says he had been keeping an eye on the Ardern-Trump meeting in New York this week.

Prime Minister Jacinda Ardern with Renée Zellweger. Photo / Pool
Prime Minister Jacinda Ardern with Renée Zellweger. Photo / Pool

He then shows a photo of them where Trump is giving a thumbs-up before jokingly adding: "Seen here after both being asked about treason with Ukraine."

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Colbert says he has a "special place in my heart" for Ardern because of her appearance on his show last year.

"She even invited me to come to New Zealand to become an official citizen of Hobbiton - not too shabby!

"This time of year in New York, you never know when you'll bump into somebody like New Zealand Prime Minister Jacinda Ardern."

Ardern then appears at the other side of the stage. "Hi Stephen."

Prime Minister Jacinda Ardern on The Late Show with Stephen Colbert, filmed in New York today. Photo / Scott Kowalchyk/CBS
Prime Minister Jacinda Ardern on The Late Show with Stephen Colbert, filmed in New York today. Photo / Scott Kowalchyk/CBS

When asked what she is doing there, she replies: "You said my name. I came out. I thought that's how the show worked."

She takes a seat and says it is a pleasure to be there.

"It's been a year since I last saw you. I invited you to come to New Zealand. You haven't been yet, which is a little awkward … We'd really love to have you."

Colbert then rifles through the pages of his schedule.

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Ardern rules out this week as she is still "trying to save the world" at the UN, and Colbert rules out the week after because of "crabfest".

Asked about the following week, Colbert says: "I'm supposed to travel with my crew to an island nation south of Australia to film a serious of comedy segments, but I might cancel that and just go to New Zealand instead."

Ardern: "I'll pick you up at the airport."

Colbert: "It's a deal. I'm going to New Zealand in October."

Renee Zellweger with Prime Minister Jacinda Ardern in New York. Photo / Pool
Renee Zellweger with Prime Minister Jacinda Ardern in New York. Photo / Pool

While waiting to go on stage movie star Renée Zellweger, a guest on Colbert's show that night, stopped by Ardern's room and they shared a hug.

A spokesman for Ardern said: "They had a warm, wide-ranging conversation. Zellweger showed her admiration for the PM, particularly her response to the Christchurch terror attack."

Renee Zellweger shares a hug with Prime Minister Jacinda Ardern. Photo / Pool
Renee Zellweger shares a hug with Prime Minister Jacinda Ardern. Photo / Pool

In her appearance on the show last year, Ardern navigated the diplomatic task of not upsetting New Zealand-US relations.

Colbert - who is no fan of Trump - asked Ardern whether leaders had laughed at Trump, rather than with him, during his address to the UN general assembly last year.

Ardern said that she had been a simple observer of the laugh in question.

She described the laugh as "a spontaneous murmur".

"There was a little laugh, then he said 'I didn't expect that response', and then there was a bigger laugh, then people laughed with him ... on the second time.

"I observed."

Colbert is a fan of the Lord of the Rings, and Ardern revealed that she had unsuccessfully auditioned for a role.

The previous time a New Zealand leader was on The Late Show, which has an average nightly viewership of 3.5 million, was when John Key went on with then host David Letterman in 2009.

He read a list of 10 things about New Zealand.

Prime Minister Jacinda Ardern with representatives from Norway, Fiji, Iceland and Costa Rica at the UN in New York. Photo / Pool
Prime Minister Jacinda Ardern with representatives from Norway, Fiji, Iceland and Costa Rica at the UN in New York. Photo / Pool

The filming for The Late Show was one of the last items on Ardern's agenda as she wraps up her trip to New York.

Earlier today, Ardern appeared on a breakfast show on CBS, and gave the opening speech at the Goalkeepers event, hosted by Bill and Melinda Gates.

She then took part in a Q&A session with them and Spanish Prime Minister Pedro Sanchez.

After that, she went to the Plaza Hotel to participate in a Bloomberg Global Business Forum panel about trade and climate change.

Prime Minister Jacinda Ardern with Facebook's chief operating officer Sheryl Sandberg. Photo / Supplied
Prime Minister Jacinda Ardern with Facebook's chief operating officer Sheryl Sandberg. Photo / Supplied

After a bilateral meeting with EU Trade Commissioner Cecilia Malmstrom, she returned to the UN to meet Belgium Prime Minister Charles Michel.

Later she was joined by representatives of Norway, Fiji, Iceland and Costa Rica announced a trade agreement to combat climate change.

She met Costa Rica President Carlos Alvarado Quesada before being filmed for The Late Show, and will finish her day with a bilateral meeting with Indian Prime Minister Narendra Modi.

Focus Live: PM Jacinda Ardern delivers speech to the United Nations

It has been a hectic few days for Ardern in New York.

Her time in New York had similarities to last year. There was political turmoil at home around Clare Curran and Meka Whaitiri, while this year it was the Labour Party's mishandling of a sexual assault complaint.

When this year's trip is finished, she would have had 18 bilateral meetings, given nine speeches, made two announcements, had two US media appearances and given one press conference.

She has rubbed shoulders with the world's most powerful leaders, including US President Donald Trump, UK Prime Minister Boris Johnson and UN Secretary-General Antonio Guterres, as well as tech executives including Facebook's chief operating officer Sheryl Sandberg, Microsoft president Brad Smith and Twitter boss Jack Dorsey.

Her two announcements were about the Christchurch Call to Action and a trade agreement to reduce tariffs on green technology and lower fossil fuel subsidies.

Prime Minister Jacinda Ardern had her first face-to-face meeting with UK Prime Minister Boris Johnson. Photo / Pool
Prime Minister Jacinda Ardern had her first face-to-face meeting with UK Prime Minister Boris Johnson. Photo / Pool

She gave speeches on climate change, including a keynote address at the UN Climate Summit, and delivered New Zealand's national statement to the UN General Assembly, which centred on the terrorist attack of March 15 and New Zealand's response to it.

She flies out of New York tomorrow.