“She had actually [worn a Michael Kors dress], I want to say it was on a tour of Australia when Prince George was a baby," Ms Ross told Express.co.uk.
“She wore a blue coat from Michael Kors and we saw that coat one or two more times.
“So she has worn the brand before, but that was the runway line. This is kind of the first time we’ve seen her in the high-street version of it.
“If you can imagine, there’s six different Ralph Lauren lines and some of them are £40 and some of them are £4000."
The Royal expert went on to reveal that while Kate has worn the American fashion labels design's before, this is the first time Kate has worn something from the 'high-street' line.
“Michael Kors is the same where we saw a runway coat, this is the first time we’ve really seen her in a high-street dress.
“But the brand has really been embraced by a lot of modern royals throughout Europe, Crown Princess Mary of Denmark, Princess Victoria of Sweden, they’ve all worn the brand before.
“So it is favoured by royals but it’s the first time we’ve seen Kate in something from the Michael Kors high-street line.”