Further demonstrating his knack at making outfits that - let's be frank here, really shouldn't work on paper - work wonders. Within sheer minutes, paparazzi shots of the singer were doing the rounds on Instagram.
Styles slipped a striped shirt beneath the geeky pull-over - sleeves rolled up for good measure - with mannish pinstripe trousers to finish.
Throw in a pair of patent candy floss pink leather loafers (Gucci, durr) and it was a look destined to grace every fan girl's Tumblr page.
For anyone out there keen to give the Kensington Palace approved trend a whirl this season, a $2,527 full-sleeve version is currently available to shop.
Princess Diana's original jumper was from Warm & Wonderful, designed by Sally Muir and Joanna Osborne.
Delivering a lesson in regal off-duty dressing, the mother-of-two layered the farm-themed knit over a sweet Peter Pan blouse with red block heels to match.
RELATED: Princess Diana's Best Style Moments Of All Time
Although Styles isn't the first A-lister to look to her wardrobe in recent weeks.
Back in August, Hailey Bieber played dress-up in some of the royal's most referenced looks for the pages of Vogue Paris.
At the hands of photographer Gregory Harris and stylist Virginie Benarroch, the model gave a millennial spin on everything from Princess Diana's now-iconic Harbour Club uniform to her weekend Sloane Ranger aesthetic.
The moral of the story? Don't throw out your cycling shorts just yet.
