Simon Howard has died, Castle Howard confirmed this afternoon (Monday).
A member of the aristocratic family who own the globally-famous estate, Mr Howard was 66.
He ran the stately home and lived there for 31 years.
A Castle Howard spokesperson said: “We are able to confirm that, very sadly, Simon Howard has died, following an ongoing illness and recent complications with his diabetes.
“We would ask for the family to be afforded privacy at this difficult time.”
Mr Howard became chairman on the death of his father Lord Howard of Henderskelfe and carried on his father’s work in conserving and restoring the Grade I listed stately home and surrounding parkland.
But at the end of 2014, he stepped down as chairman and chief executive of Castle Howard Estate Ltd.
He and his family moved out of Castle Howard as elder brother Nick Howard became non executive co-chairman and Nick’s wife Victoria became executive co-chairman.
They moved in and took over responsibility for day-to-day running of the house and estate, which is visited by nearly 250,000 people a year and is known throughout the world as a filming location for Brideshead Revisited and Bridgerton.
Nick Howard said at the time: “Simon has worked tirelessly for Castle Howard. I cannot thank him enough for what he has achieved during his tenure.
“Were it not for his extraordinary commitment, we would not be in a position to carry on his good work.”
Last November, Simon Howard was found to have committed indecent assault and incited a child to commit an indecent act by a York Crown Court jury.
The aristocrat was in his 20s when he abused the girl in the gatehouse of the estate in 1984.
Mr Howard, by then living at Wellham Road, Norton, Malton, was found not fit to stand trial due to a brain injury he suffered in a fall following his arrest.
However, he was placed on the sex-offenders’ register for five years, which is automatic for such offences.