Britain's Zara Phillips thinks it would be "sad" for New Zealand to change their flag.
The 34-year-old Olympian insists the current design - a navy background with red stars and the Union Jack in the top corner - is "great" and she hopes it doesn't change when a referendum on the standard takes place next year.
Zara - who is the daughter of Princess Anne and her first husband Captain Mark Phillips - told TVNZ: "You know when you look at the flag you know that it's Kiwi. It would be sad to change it I think.
"I guess it's great the way it is."
Zara has breached royal protocol by speaking about constitutional matters and her remarks have been slammed as "quite unsuitable".
Royal biographer Michael Thornton told the Daily Mail newspaper: "I find Zara's comments quite unsuitable.
"I know her mother, Princess Anne, and she does a splendid job of keeping her trap shut on important matters. I think that Zara could do with taking a leaf out of her book.
"There are certain things which the Royal Family should not comment on, and this is one them. It's beyond the boundaries, particularly for a junior member of the royals, and liable to cause offence."
And it seems her comments have also sparked outrage amongst local residents.
One person wrote on Twitter: "Queen's granddaughter Zara Phillips against New Zealand flag change . . . well that's another reason to change (sic)"
Another slammed: "Zara Phillips calling for the flag to stay is the only good reason I've heard to change it. New Zealanders' opinions only, please.(sic)"
New Zealanders currently have until July 16 to suggest a new design for the flag. A panel of 12 will then narrow down a shortlist for the public to vote on.