The Duchess wearing her TopShop frock
05/16/2013 at 11:00 AM EDT
officially in nesting mode?
If her recent trip to the Design Centre in Chelsea Harbour
is any indication, the answer is yes.
The seven-months-pregnant Duchess of Cambridge
, 31, was spotted shopping at the ultra-posh interior design center on Tuesday, where she checked out at least one fabric swatch, and took time to refuel at the public café, right alongside other shoppers.
"She just sat in the atrium like everyone else," an onlooker tells PEOPLE. "She was very polite and really nice – just totally normal. I didn't know it was her at first. I just thought, 'You look a lot like Kate Middleton.' Then it kind of dawned on me."
"She had a cappuccino and a banana muffin," adds the source. "It's not every day you see the future Queen of England sitting down in a café eating a muffin!"
Kate – who recently hired
one of the Queen's longstanding housekeepers for her and Prince William
's new home inside Kensington Palace, which they plan to inhabit early this fall – also stopped into Mulberry Home and looked at a swatch of Twelve Bar Stripe
fabric in sand and rose before calling it a day.
"She was nice, but I think she was a bit tired," says another source. "[She] had done a lot of shopping for someone who is so heavily pregnant. She didn't really say anything. She just pottered around looking at the fabrics. But she seemed really nice."
Reporting by PHIL BOUCHER