Shand was organising fundraising for his conservation charity when he fell and seriously injured head
The Duchess of Cornwall's brother died in New York after an accident, Clarence House has said.
Mark Shand, 62, was celebrating the conclusion of a fundraising campaign for his conservation charity when he fell and injured his head early on Wednesday morning. He was rushed to hospital but died on Wednesday.
Clarence House said the Prince of Wales and the Duchess of Cornwall were "utterly devastated" by the death of her brother. Clarence House, which deals with the affairs of the Prince of Wales and the Duchess of Cornwall said: "It is with deep sadness that we have to confirm that the Duchess of Cornwall's brother, Mark Shand, has today passed away in New York. Mr Shand died in hospital as a result of a serious head injury which he sustained during a fall last night. The duchess, the Prince of Wales and all her family members are utterly devastated by this sudden and tragic loss."
Shand was the youngest child of Bruce Shand and Rosalind Cubitt. He was brought up with his elder sisters, Camilla and Annabel, near Lewes, East Sussex.
He was educated at Milton Abbey School in Dorset but was expelled for smoking cannabis. In 1990 he married Clio Goldsmith; they have a daughter, Ayesha.
He wrote about travel, conservation and India. His books included Travels on my Elephant and River Dog.
Clarence House described Shand as "a man of extraordinary vitality, a tireless campaigner and conservationist whose incredible work through the Elephant Family and beyond remained his focus right up until his death".
Shand was chairman and founder of Elephant Family, a charity which worked to support Asian elephants in India. The charity raised £950,000 on Tuesday night shortly before Shand's injury.
The chief executive of Elephant Family, Ian Walkden, said: "We have lost the head of our family. Mark Shand was a true force for conservation. He was both a legend and an inspiration to us and above all our great friend. We will miss him always."
Walkden said the Elephant Family had delivered £6m of support to the conservation of Asian elephants and was responsible for creative and inspirational fundraising campaigns.
Tuesday night was the culmination of a spring fundraising campaign for Elephant Family which featured the Big Egg Hunt, sponsored by Fabergé. The hunt involves 200 giant eggs hidden around New York which are decorated by famous artists and designers and sold at auction.
An egg Shand commissioned for the event was of Humpty Dumpty, and was created by The Prince's Drawing School and signed by the Prince of Wales and the Duchess of Cornwall. The work was called "The Royal Egg — Humpty Dumpty, 2014".
The eggs were sold at auction for $1,600,000 (£950,000). Guests included Diane von Furstenberg, Hayley Bloomingdale, Princess Eugenie of York and Princess Ira von Fürstenberg.
The auction was followed by an afterparty at the Diamond Horseshoe nightclub at the Paramount Hotel in West 46th Street, close to Times Square but Shand and friends continued to a late night bar. A spokesman for New York Police Department said an ambulance was called to Gramercy Park Hotel at 3am and Shand was taken to Bellevue Hospital where he died.
On the Elephant Family website, Shand described how he "fell in love" with an elephant called Tara in Madras. He bought Tara and rode her across the north-eastern states of India. It was this journey that inspired his book Travels with My Elephant and prompted him to start Elephant Family in 2000.