On Thursday, Crown Prince Tupouto'a 'Ulukalala will marry his second cousin, Sinaitakala Fakafanua.
One member of the royal family, Princess Frederica Tuita, has publicly called on them to marry outside the family.
Prominent member of the Tongan community in Auckland, Will Ilolahia, tells Bruce Hill many Tongans are against the marriage of such close relatives.
Presenter: Bruce Hill
Speaker:Will Ilolahia, a New Zealand Tongan community leader
ILOLAHIA: It's a major issue because basically traditionally we still have quite a strong Papuan regard to brothers and sisters, and in the Tongan society we don't have a word for cousins, cousins are actually brothers and sisters. So this is quite a significant move against even tradition, and I think that's probably why the present King is not for it.
HILL: You say the present King Tupou the 6th is not for it, has he sort of made that public or is it just generally known around the place?
ILOLAHIA: It's known, it's known amongst those of us that are close to the family, but it's also known. And we've also heard that [Princess] Pilolevu and I think the Queen is going to be out of town at the same time, so we're not quite sure of their support or their stance, because they've had similar situations previously of a princess having some close marriage to another noble from Hihifo. The offspring was obviously there was something wrong biologically.
HILL: There's a bit of a history of royal families, not just the Tongan royal family, but royal families generally marrying within royalty and often within their own family. In Europe I'm thinking in particular of the Hapsburg family?
ILOLAHIA: Yeah and I can understand the whole thing about keeping the royal line, I mean that's just probably part of the whole royalty thing. But I think just as Tonga now has brought in new nobles who have no sort of hereditary titles and that kind of stuff, perhaps this is the way to go, because the tradition is that the royal family are married within the upper echelons so to speak of Tongan society, because I know myself I'm actually a victim of the situation in a sense, and a good victim I might add Bruce because my mother couldn't marry my father because he was a commoner. So that's the reason why I was born here in New Zealand. So I know what it's like.
HILL: Is there really a genetic risk if cousins marry? I mean we have an incest taboo and that's across all cultures around the world, brother and sister can't get married, we know the results genetically are really bad. Is there really such a risk if cousins marry though?
ILOLAHIA: Well like I said we've already had a situation of one of the princesses who actually was an offspring of married within the close bloodlines, and so that's probably where they should have learnt from that situation. I mean it's also a concern that whoever's this offspring's going to be is going to be the future king or queen. So that's another concern, if we are going to try and continue on with maintaining our royal families, which were from 2000 BC.
HILL: Isn't it a bit controversial to even raise this sort of thing? It sounds like the sort of thing that people sort of talk about in hushed whispers rather than actually sort of in public?
ILOLAHIA: It is and I mean I've put my head on the chopping block by talking to you Bruce, but I think it's important enough that we need to speak out. And several of us here in New Zealand have already made it known, I mean even Princess Frederica Tuita has come out on a blog basically saying the same thing, so there is concern.
HILL: With the royal wedding there's going to be a lot of cultural expectations on the Tongans living overseas in New Zealand and Australia and even the United States to come back to Tongan and to give gifts and to participate in this. Are attitudes towards these expectations changing among perhaps the younger Tongans living overseas?
ILOLAHIA: Yeah I think because most of us overseas now have actually taken on our host cultures, mores so to speak in regard to New Zealand being more New Zealanders than Tongans. At the same time we do understand our cultural heritage, we still call Tonga our home and so some events like this in some ways especially in Tonga at this particular time, especially in the way the country's going at the moment, me personally I think it's of benefit in regard to bringing some income into ... I mean I know of plane loads leaving from New Zealand and are going to come up just for the wedding.