US talkshow host Stephen Colbert's journey to become the "newest New Zealander" has come to an end.

The last of Colbert's five New Zealand-focused episodes will air tonight on The Late Show (US time). In a preview, Colbert said it would feature New Zealand's natural beauty.

"New Zealand is a hard land to leave," said Colbert ahead of the final episode.

Tourism NZ estimated that the week-long exposure for New Zealand was worth around $5 million in advertising.

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That was a "significant return on investment" for the $100,000 it chipped in to help host Colbert last month. Around three million people watch Colbert's show.

The publicity coup came about after Tourism NZ and NZ Trade and Enterprise worked together to offer Colbert a gift when Prime Minister Jacinda Ardern first appeared on The Late Show in September last year.

Ardern offered to make Colbert, a Lord of the Rings fanatic, a citizen of Hobbiton - an offer it appears he accepted.

Colbert called his series on this country "The Newest New Zealander", joking that he wanted to get citizenship here because of the political turmoil in his home country.

During six days' filming in New Zealand, he spent time with Ardern, who has appeared on his show twice and whom he calls a friend.

American late night talk show host Steven Colbert during his trip to New Zealand. Photo / CBS
American late night talk show host Steven Colbert during his trip to New Zealand. Photo / CBS

Fulfilling a promise made on an appearance on The Late Show, Ardern personally picked him up at Auckland Airport. They had a "state dinner" of barbecue sausages and white bread at Ardern's home.

Colbert dabbled in more New Zealand cuisine in Wellington, trying marmite on toast and a spaghetti toastie - prompting him to ask whether New Zealand's best chefs "were as skilled as my sophomore room-mate".

The talk show host also learned to play rugby, assisted by former All Black Piri Weepu, former Sevens captain DJ Forbes and broadcaster Laura McGoldrick. And he filmed and starred in a mock spin-off of the Lord of the Rings series.

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Former National Prime Minister Sir John Key also appeared on The Late Show in 2009, when it was hosted by Colbert's predecessor David Letterman, as a marketing stunt to promote New Zealand as a destination.