Police were investigating the suspicious death of Suzy Healey, 39, the daughter of Malcolm Healey, who has a fortune of £750m.
Ms Healey, a mother of two teenage girls, was discovered at Ellerker Hall in East Yorkshire. She spent her time providing homes for animals rescued by the RSPCA.
Her home stands in 10 acres of land, some of which she had converted into stables, in East Riding village. But she lived in a modest outbuilding which she had converted into a cottage, not in the Hall itself. Yesterday, the mansion remained sealed off by police.
Ms Healey's father made much of his fortune after he sold his Hygena kitchen business. His brother is the millionaire Eddie Healey, who along with another developer, Paul Sykes, turned a derelict site outside Sheffield into Meadowhall shopping centre. Its £1.17bn sale in 1999 netted him about £420m for his stake. The Healey brothers appeared in 21st place in the Sunday Times Rich List with a joint fortune of £1.45bn.
While Ms Healey lived a private life, predominantly on her property which she transformed into a nature reserve, some of her family have gained attention for a more extravagant lifestyle. In 1990 Ms Healey's cousin Annie was married, with the pop group Five Star performing at the reception. Belinda Carlisle has performed at another family party.
A post-mortem examination was due to be carried out on Ms Healey's body last night.
A spokeswoman for Humberside Police said: "At 8.30 yesterday morning Humberside Police received a call from a member of the public expressing concern for a friend. Police attended an address in Main Street, Ellerker, and discovered the body of an adult female in the house.
"The house has been cordoned off and scenes of crime officers along with detectives are currently making inquiries."
It was understood that the death was being treated as a domestic-related incident.
Chris O'Connor, who lives in nearby South Cave, said the news had shocked the area. She said: "She was a very nice person, a nice good-looking young lady. She was only in her thirties and had two children. It is so terrible."
Speaking at the scene, Detective Inspector Nigel Sawyer said: "We were called shortly after 8.30 yesterday morning." He said a friend had contacted police when she was unable to raise the woman at her home. "Police officers from Humberside Police entered the premises where they found the body upstairs," the detective added.
A man aged 37 was arrested on suspicion of murder in the Scarborough area by detectives from North Yorkshire Police yesterday.Reuse content