Camilla received the devastating news "on a glorious early Spring day in Scotland" with her husband Prince Charles, when "the shrill ring of the telephone broke the magic".
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The Duchess of Cornwall has spoken for the first time about the death of her brother
In a powerful article published in The Times, the Duchess said, "An anguished voice on the other end told me that something terrible had happened to my brother; my indestructible brother, Mark. Surely nothing could have happened to him?
"He was in New York raising money for his beloved elephants, but an unfamiliar pavement had claimed his all-too-short life following a hugely successful auction for The Elephant Family, a charity he co-founded in 2002.
"My charismatic and sometimes infuriating brother, who had survived tsunamis, shipwrecks, poisoned arrows and even the fearsome Komodo dragons, was no longer with us."
The Duchess of Cornwall pictured with her late brother, Mark Shand
Speaking ahead of a memorial service for Mark, 62, due to take place on 11 September, Camilla recalled their "idyllic childhood living in Sussex under the South Downs".
She wrote, "It was happily before the advent of political correctness and health and safety, to neither of which Mark in his later life ever conformed.
"He metamorphosised from rather a bad-tempered, fat child into a golden boy, blessed with good looks, charm, and a 'devil may care' attitude."
Heartbroken Camilla and Prince Charles at Mark Shand's funeral
Camilla then wrote of her brother's passion for elephants, which began in 1988 on a visit to India, where he rescued a female elephant named Tara.
"They embarked on a thousand mile journey across the north of India (which he recalls in his best-selling book, Travels on my Elephant) and by its finale he was in love," the Duchess said. "This was the start of his life-long passion for India and his quest for the survival of the Indian Elephant."
In her touching conclusion, Camilla said, "They say that elephants never forget; Tara never forgot him and neither will we…"