Queen Camilla marked Heywood Hill's 90th anniversary with a visit to the independent Mayfair bookshop on Tuesday.
The store is renowned for its personalised reading consultations, during which customers share their literary tastes to receive a bespoke year-long book subscription.
Camilla, a passionate reader who serves as patron to several literary organisations, took part in one of these sessions.
Deputy bookshop manager Harriet Bibby guided the consultation, asking the Queen to identify her all-time favourite reads.
The visit also held personal significance for Camilla, whose late father Major Bruce Shand was himself a customer at the west London establishment.
Elizabeth Jane Howard's Cazalet Chronicles topped her list, which she called her "absolute favourite", followed by Alexandre Dumas's The Count of Monte Cristo.
"Goodness me, there are so many after that. I'm thinking of them all, but they all seem to come up at the same time," she told Bibby.
Amor Towles's A Gentleman in Moscow also earned praise as "just wonderful", alongside works by William Boyd and Anthony Horowitz.
The Queen estimated her reading habits split roughly 80 per cent fiction to 20 per cent non-fiction.
When asked about genres she avoids, Camilla responded without hesitation: "I hate sci-fi."
Pronouncing it "sky-fi", she laughed and added: "That, I'm afraid, is not my favourite. I'm sure a lot of people love it, but, um... No science fiction. No, I can't do that, you have to have some things you love and some things you really don't love, and that really is one I don't love."
During her tour, Camilla rolled up her sleeves in the packing room, where she had been added to the staff rota as "CR" with a crown symbol beside her name.
She assisted two full-time packers by wrapping The Renoir Girls by Catherine Ostler in brown paper and finishing it with a blue ribbon bow.
Staff also presented her with a large world map displaying blue and yellow flags representing subscribers across more than 80 nations.
After completing her tour of the shop's four main rooms, Camilla unveiled a plaque officially renaming one space the "Queen's Room".
Chief executive Nicky Dunne accompanied her throughout the visit, noting her father's connection to the establishment and asking whether she had visited as a child.
"I'm sure I did come here when I was much, much smaller," the Queen replied.
A crowd had assembled outside with cameras ready during her time in the shop.
Camilla departed through the front entrance and crossed the zebra crossing to Shepherd Market, where she met and chatted with local business owners and traders in the upmarket backstreet.
