62-year-old Mark Shand was the brother to Camilla, Duchess of Cornwall.
Clarence House confirmed Shand's passing:
"It is with deep sadness that we have to confirm that The Duchess of Cornwall's brother, Mark Shand, has today passed away.
"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."
At the time of the accident, Shand had just finished presiding over a charity auction for the Elephant Family, a charity dedicated to preventing the extinction of the endangered Asian elephant. He slipped while smoking a cigarette outside the fundraising party.
Shand established the Elephant Family charity in 2002. The charity remembered Shand as "a true force for conservation."