There are a few fashion rules that pretty much everybody can recite verbatim. No white after Labor Day. Always match your belt with your bag. And, of course, never, ever mix navy and black. Although these rules may sometimes make sense, they were also made to be broken. And Kate Middleton just reminded the world why.

For years, Kate Middleton’s fashion choices have been a masterclass in polished, princess-perfect style. But her look on March 15 at the Six Nations match in Cardiff? A quiet departure from the norm—one that signals a shift in how she’s approaching fashion altogether.

It’s been a confusing few months for anyone obliged to write about Kate Middleton ’s wardrobe for a living. First, there was a not-quite announcement, through a source quoted in The Times, that the Palace would no longer be issuing details on the Princess of Wales’s outfits.