And now we know the answer it has only added to the magic of the whole occasion.
Australian Vogue first reported that Robbie’s off-the-shoulder gown might have been designed by Oscar de la Renta, but now The Courier-Mail has reported Robbie in fact wore a vintage gown first worn by her mother, Sarie Kessler, 30 years ago.
Robbie had the dress altered by Australian designer Casey Tanswell in the days leading up to the ceremony, a “source” told The Courier-Mail.
“(Tanswell) had been approached by a friend to do the alterations,” the source said.
“She didn’t know it was Margot until she turned up at her home for the fitting.”
Scroll down to see more examples of Tanswell’s bridal work.