On a trip to London's TopShop on Oxford Street Wednesday, Kate picked up a few bags of new clothes, including Lovestruck's lightweight Deidre dress.
The clothing company said that the floral frock (which retails for 37 British Pounds, or about $56) is not maternity wear but has a "practical elasticated waist enabling the dress to expand with the bump."
"We are especially pleased that the duchess has selected a dress that accommodates her maternity needs without feeling the need to buy from a specific maternity range," head designer Erika Shaw says.
Kate surprised fellow shoppers while at the store. "I turned to see Kate Middleton browsing right aside me and smiled at me," Layla Maan tells PEOPLE
Maan says Kate, 31, soon moved off towards the personal shopping area.
"I am usually invited to the personal shopping area but security was there this time and it was all very undercover," adds Maan. "I have worked in media and national press for over 10 years and have never felt star struck like that! She was simply elegant."
A source at the store adds, "She was in our VIP area, so she could try on all the dresses in total privacy. When she left it was all bagged up. She didn't buy loads of stuff, just a couple of bags. She was really nice and friendly to everyone. She wasn't at all 'princessy'."
Another source at the store tells PEOPLE, "I saw her and she was really nice. She looked really beautiful. She was just browsing around the floor. She walked all around. She was alone. I was really surprised she was shopping alone as you'd think she would have lots of security with her. But she was just walking around like anyone else.
TopShop would not comment on Kate's shopping trip.