William and Kate have sympathised with the Duchess of Cornwall after the sudden death of her brother, following a fall in New York.
The Duke and Duchess, who are coming to the end of their tour of Australia and New Zealand, passed on their sympathies to Camilla who was left "utterly devastated" after Mark Shand died from a serious head injury on Tuesday night.
Kensington Palace said: "The Duke and Duchess of Cambridge were saddened to learn this morning of the tragic death of Mark Shand.
"Their thoughts are with the Duchess of Cornwall and her family at this time."
Mr Shand, 62, was taken to hospital after reportedly slipping while lighting a cigarette and hitting his head on the pavement outside an after-party for a charity event.
He was in New York for an auction at Sotheby's in aid of a charity for underprivileged children and the Elephant Family, of which he was chairman, which aims to save the endangered Asian elephant from extinction in the wild.
Camilla and the Prince of Wales, who are preparing for a high-profile tour of Canada next month, are believed to have received the bad news at their Birkhall home in Scotland.
A Clarence House spokesman said yesterday: "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.
"Mark Shand was 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."
Tributes poured in for Mr Shand, a conservationist and travel writer who was known for his love of adventure and fondness for glamorous women.
A spokesman for the Elephant Family described him as a "true force for conservation", "both a legend and inspiration and above all our great friend".
Dan Bucknell, head of conservation and campaigns at the charity, said Mr Shand had "infectious enthusiasm" for his work for Asian elephants.
He told the BBC: "He did so much for the charity, he was a very fun-loving, warm-hearted generous guy, who was always very hands-on with all the events that we did and we are going to miss him very sorely."
Mr Shand had been in New York for the finale of the month-long Big Egg Hunt NYC by Faberge, which saw egg sculptures sold to the highest bidder and raised raised 1.6 million dollars (£950,000).
Mr Bucknell said the day after the event "should have really been one of celebration", but staff were left "incredibly shocked, numbed and incredibly stunned" by the sad news.
Mr Shand, Camilla's only brother, wrote numerous books and featured in documentaries, with elephants and India as recurring themes.
The adventurer's book Queen Of The Elephants won the 1996 Thomas Cook Travel Book Award and the Prix Litteraire d'Amis, and was made into a BBC documentary.
During his youth he was a renowned nightclubber who was expelled from Milton Abbey School in Dorset for smoking cannabis and had stints as a rally driver and bobsleigh competitor.
His father, Major Bruce Shand, decided to send him to Australia after he was expelled and he stopped off in India, where his love of elephants first took hold.
Later in life he was romantically linked to the likes of Bianca Jagger, Jackie Onassis's sister Lee Radziwill and Jackie's daughter, Caroline Kennedy.
In 1990 he married former French actress Clio Goldsmith, the niece of billionaire entrepreneur Sir James Goldsmith and the cousin of Jemima Khan and Tory MP Zac Goldsmith.
The couple, who split in 2009, have a daughter together called Ayesha.
Heiress and campaigner Ms Khan posted her condolences on Twitter, saying: ? "RIP Mark Shand: Best man, godfather to my son & my cousin's ex".
Ms Khan's ex-husband, former Pakistan international cricketer and politician Imran Khan, tweeted: "Shocked & saddened to learn of the death of one of my closest English friends, Mark Shand, in New York where he was raising funds 4 charity."
MP Mr Goldsmith added: "Conservation has lost a hero today. RIP the great and wonderful Mark Shand."
Television personality Piers Morgan said: "What an awful, tragic thing to happen. Poor Camilla & her family incl @tomparkerbowles."
American actress Kristin Davis, who has campaigned over the plight of orphaned African elephants, tweeted: "I am heartbroken over the death of Mark Shand,He did tremendous good with his life thru @elephantfamily + so much else What a horrible loss."