Ardern spoke of the Queen's interest in New Zealand's current affairs and said King Charles had a similar interest.
"Over the years, [Charles' involvement in politics] has always been at the level of where you would expect a future king to be interested," Ardern told du Plessis-Allan.
As a prince, King Charles expressed his opinions publicly on climate change and a number of other issues, which was at times controversial due to a precedent for royals to remain politically neutral.
"[Royals] do have an interest in what's happening; current events and issues that are top of mind for New Zealand," Ardern said.
She said she had met King Charles on a "number" of opportunities, as recent as this year in Europe, where he had shown a "genuine affinity" for New Zealand.
Ardern said he was particularly connected to the country through his work with The Prince's Trust, a charity for vulnerable young people.
"I think about the times when I spoke to the Queen, it was during things like lockdown. Of course, when we've had members of the royal family, such as Prince William, it was in the aftermath of March 15."
Ardern said she was unsure of when she would speak to the country's new king, as he would be currently involved in establishing the UK's new government.