Bronagh Key has chosen a top bridal designer to design her outfit for the Royal Wedding on April 29 - a decision that has raised eyebrows.

Kevin Berkahn, once labelled the "bridal king", said he was privileged to be designing the outfit, but stayed tight-lipped on the details.

Other fashionistas expressed their expectations, however.

Ricardo Simich, a fashion expert and former colleague of Berkahn, said he was surprised. "He's a fantastic designer for brides, but for mother of the bride and guests - I don't think so."

"If she wants to go classic, Berkahn is probably not [the right designer] but if she wants to stand out then she's picked the right man," Simich said.

Berkahn, who has been designing clothes for more than 40 years, is famous for his bold designs.

One of his most memorable is a green full body dress and wig designed in 1973.

He was awarded the Member of the Order for services to fashion and the community in the Queen's Birthday honours last year.

Liz Mitchell, who was designing a dress for another guest of the wedding, said Berkahn had a lot of experience.

"I think he's had a lot of experience in dressing women in high-profile positions and couture one-off dresses. He's quite a classic kind of designer."

Mitchell expected Bronagh to wear a classic design.

"She's the Prime Minister's wife and I think she does need to wear something quite formal and appropriate for the wedding ... fascinator hats, little jackets, cocktail type dresses to the knee, a lady-like look."

Prime Minister John Key and Bronagh will attend the wedding with Governor General Sir Anand Satyanand and his wife Susan, Lady Satyanand - believed to bethe guest for whom Mitchell is designing.