Sarah Ferguson's uncle "die within minutes" following an allergic reaction.
The Duchess of York revealed that her father's brother John passed away at the age of ten after suffering an allergic reaction to a crab sandwich while at Brancaster Beach in North Norfolk, and confessed that her dad was "never the same" following the tragic accident.
Speaking to ITV News she said: "My uncle, age 10, died of a crab sandwich at Brancaster Beach and my father was never the same after that. And my grandmother never forgot John - he was called John."
The 59-year-old royal recently became a patron of the Natasha Allergy Research Foundation - an organisation which promotes allergy research and safety - and explained that it wasn't until she started working with the charity she realised the effect her uncle's death had on her grandmother.
She said: "It wasn't until working with Nadim and Tanya [Ednan-Laperouse,] and being with them that I suddenly realised.
"Can you imagine what my grandmother went through? In those days, forget it. He was out on the beach with [his] nanny - he wasn't even with my grandmother or father - he was on his own with [the] nanny and he died within minutes."
The Natasha Allergy Research Foundation was named after Natasha Ednan-Laperouse, who died in 2016 at age 15 after unwittingly eating food that contained sesame seeds at a Pret a Manger in Heathrow Airport.
Fergie previously tweeted: "So proud to have been asked to be patron of @NatashasLegacy. Today we're delighted to welcome Government announcement of Natasha's Law to support allergy sufferers but there is much more work to do to promote research. (sic)"