The Duchess of Cambridge was stunned by the new entrance to the Victoria and Albert Museum, as she attended a ceremony to open the £56.4 million Exhibition Road Quarter.
Kate, who wore a nautical Gucci dress, mouthed "Wow" as she walked into the Sackler Courtyard - the world's first all-porcelain public courtyard, paved with 11,000 hand-made tiles in 15 different patterns
The Duchess, who studied History of Art at university, toured the V&A's new development, including the Sainsbury Gallery - a huge underground space that was created by digging 59ft (18m) under the museum.
The facility, which was largely funded by private donors, was completed in four years by British architect Amanda Levete and her practice, AL_A.
Ms Levete, who won the contract for the project in 2011, said: "It's an absolute honour to have the Duchess of Cambridge opening this building, and I feel very proud of the work my team have done."
The architect, who has recently been nominated for a CBE, said Kate was "quite stunned" when she first emerged into the porcelain courtyard because the "sun came out and the courtyard was glistening".
The Duchess also unveiled a commemorative plaque in the Sackler Courtyard.
V&A director Dr Tristram Hunt said: "I think she was wowed by the architecture, and she was really interested in the engineering - how we dug down and yet kept the walls upright and didn't break a single glassware or ceramics."
The former MP added: "It's also a huge day for the museum; it really revives our original mission, which is the notion of Albertopolis, spreading out on to Exhibition Road."
The first public exhibition will launch in September in the Sainsbury Gallery, with seven nights of opera featuring a different show each night.
Kate, who is a patron of The National Portrait Gallery, also congratulated donors during a short reception to meet guests involved in the project's delivery.
Sir Tim Sainsbury, 85, a trustee of the Victoria & Albert Museum, said: "I think, like everybody else, the Duchess was immensely impressed by the scale and column-free big heights of the Sainsbury exhibition space.
"I think she genuinely enjoyed herself - she even said she's looking forward to many more future visits."