Queen Camilla shared a playful moment with a group of amused primary school pupils as they crammed into a traditional red telephone box.
The Queen issued the challenge of "how many" could fit in the classic British landmark while visiting the Dulwich Picture Gallery in south London on Thursday.
The 78-year-old royal left gallery director Jennifer Scott and onlookers stunned by spontaneously joining the youngsters from Dulwich Village Infants' School inside the cramped space.
"Let's see how many we can get in there," Camilla exclaimed, before watching the six and seven-year-olds pile in.
Queen Camilla amused onlookers by challenging schoolchildren to see 'how many' could fit in a phone box
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After observing the children bundling themselves into the iconic British landmark, the Queen declared, "let me come in", and proceeded to join them inside.
The royal's impromptu participation prompted an astonished response from Ms Scott, who exclaimed: "Oh your Majesty, we weren't expecting that! What a treat."
The visit commemorated the unveiling of the gallery's new £5million Artplay Pavilion and sculpture garden.
As rain began falling, the Queen explored the indoor play facility, testing equipment and examining various corners whilst meeting Open Art project supporters and gallery trustees.
The Queen then joined the eight giggling school kids in the British landmark
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Her playful demeanour continued when pupils rushed into the pavilion.
"They're coming in!" Camilla observed as youngsters scrambled through tunnels and ascended the indoor slide.
However, the Queen declined an opportunity to continue her fun-loving streak when shown a slide at the site.
She firmly declared: "I'm not going down that slide!"
'I'm not going down that slide!' Queen Camilla declared, declining to continue her creative streak
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The Queen sported an elegant monochrome ensemble for the occasion, wearing a black and white collared frock paired with silver heels.
She accessorised with multiple gold chain bracelets, including a Van Cleef & Arpels piece featuring turquoise petals valued at £5,350.
Before departing, two pupils presented Camilla with a gallery gift bag and flowers.
"Thank you very much. I'm very lucky," she responded graciously.
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The Queen was visiting the Dulwich Picture Gallery in south London
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Dulwich Picture Gallery holds significant historical importance as the world's first purpose-built public art gallery, having welcomed visitors for over two centuries. The newly opened sculpture garden offers free public access.
The gallery's outdoor attractions include Harold Offeh's sculpture "Hail the New Prophets," a slide drawing inspiration from 1980s spacecraft designs.
The Queen appeared particularly taken with the Lovington sculpture meadow, which showcases various artworks, including an earthwork influenced by Rembrandt's "The Girl At A Window".
Across the capital, Prince William and Princess Kate were visiting the Natural History Museum.
While there, Kate showed off her new "Disney Princess-like" blonde locks.