Mark Shand - the brother of the Duchess of Cornwall - was the chairman of Elephant Family, which aims to save the endangered Asian elephant from extinction in the wild.
In a statement, the charity said it had "lost the head of our family".
The statement on the charity's website reads: "Today we have lost the head of our family. Mark Shand was a true force for conservation.
"He was both a legend and inspiration and above all our great friend. We ask at this time that people’s thoughts are with his loved ones. We will miss him always."
More top news
Theresa May has launched her bid to become the next leader of the Conservative Party.
The government is set to announce that David Cameron's successor will make the decision on whether to expand Heathrow or Gatwick.
Michael Gove is to stand for the Conservative Party leadership, saying he does not believe Boris Johnson can "provide the leadership".