Prime Minister Jacinda Ardern has endorsed the humble mullet in an Instagram post celebrating the All Blacks' win against Ireland in their Rugby World Cup quarter-finals match in Tokyo at the weekend.

She captioned a photo of All Blacks starting centre Jack Goodhue clapping Nepo Laulala on the shoulder, his glorious mullet on full display.

"And that's a brilliant win ... for the All Blacks, and mullets everywhere. Go the @allblacks! We're right behind you for the semis," she captioned the photo.

On Friday Goodhue revealed his business up front, party in the back haircut made him faster.

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"I'm not getting rid of the mullet - you can ask this every week or something but it's not going. There's actually scientific evidence that shows that it actually makes me faster, it was done at Harvard," he said.

When quizzed by teammate Sam Whitelock whether he would trim his locks for his upcoming wedding, he referenced the Women's Day article which said it would be revealed on the big day.