Kate Middleton just broke one of her style rules for an official engagement

We didn't expect to see this...

By Alexandra Whittaker

This article originally appeared on InStyle US

Let's cut to the chase: Kate Middleton's sense of style is downright enviable. Between the vibrant coats and the tasteful dresses, she steps out wearing prim and proper looks on a daily basis, and royal fans can't get enough of it. But sometimes, even Middleton needs to keep things casual, as she demonstrated clearly on Wednesday.

In an uncharacteristic move, Middleton wore athleisure while out on an official royal visit.

She traded in a scarlet Boden peacoat she wore earlier in the day for a pair of black and white gym trousers, a white zip-up jacket, and trainers. In true Middleton fashion, her delicate teardrop earrings remained on despite the laid-back outfit.

While her look might raise eyebrows, it was totally appropriate for her day.

The Duchess of Cambridge wore the sporty ensemble while visiting the Wimbledon Foundation's Junior Tennis Initiative as a patron of Wimbledon. There, she met students who benefited from the foundation's free tennis coaching. During her trip, she also showed a better glimpse at her growing baby bump.

While royals don't often step out so casually, on rare occasions even they like to indulge in comfy athletic gear. Middleton has, in fact, worn gym wear as outerwear before, and just a few weeks ago, Meghan Markle wore your favourite go-to gym hairstyle during a royal occasion.

Since Middleton is dressed down for such a sport-specific event, it's really no surprise that she played a bit of tennis herself while at the event. She even helped kids practice their drills by throwing balls to them.

Kensington Palace tweeted out a photo of Middleton in a huddle with kids while holding a neon blue and yellow racket of her own.

Looks like dressing the part paid off.