After popping into Lacoste to pick up some new pyjamas for her one-year-old son, Kate was seen shopping in a few of her favourite stores - Ralph Lauren, Temperley and Gucci.
"Kate came in on Sunday on her own, just like anyone else, and browsed the sales racks," a sales assistant told the newspaper.
"At first I didn't recognise her, I couldn't believe it was Kate. She was very friendly."
So far, so normal, but if you're trying to imagine Kate weighed down with shopping bags during her tip - think again. It's thought she had her purchases couriered straight to Kensington Palace.
Perhaps Kate was looking for an outfit to wear to her friend's wedding?
According to Vanity Fair, the duchess is joining Prince William and Prince Harry on a trip to Italy to see Charlie Gilkes, who attended Eton and now runs nightclubs and restaurants in London, marry Anneke von Trotha Taylor.
A source told the magazine: "The [Cambridges] are really looking forward to it and William and Kate are planning to leave Prince George with Kate's parents so they can go and have a good time."
Let's just hope the Queen doesn't hear about her recent shopping spree...
More of Kate's smart style below: