11th Duke of Marlborough.

Born April 13, 1926; Died October 16, 2014.

John Spencer-Churchill, the 11th Duke of Marlborough who has died aged 88, was a friend of Prime Minister David Cameron, a cousin of Winston Churchill and a distant relative of the late Diana, Princess of Wales.

The owner of the opulent Blenheim Palace estate, which is worth an estimated £100 million, he was best known in the public mind for the extensive efforts he made to protect the estate from falling into the hands of his "black sheep" eldest surviving son Jamie Blandford, Marquess of Blandford, who will inherit one of Britain's most prestigious aristocratic titles.

The 58-year-old, rehabilitated, will become the 12th Duke of Marlborough after a long and public battle with heroin and cocaine which saw him feature regularly on newspaper front pages. Described by some as "the wayward peer", he spent £20,000 in just four months to pay for his drug binges. He had several spells in prison, mainly for driving offences, and was in and out of court throughout the late 1980s and 1990s.

He became estranged from his father, who all but disinherited him from the family fortune.

In a bid to safeguard the Blenheim Palace estate from the Marquess's excessive behaviour, the late Duke won a High Court battle in 1994 to ensure his son did not won control of the family seat, where wartime premier Churchill was born.

After the ruling, the Duke of Marlborough said of his son: "I think there have been black sheep in every family and there's nothing new about that.

"We have had some good 'uns and some bad 'uns. He's had every chance, hasn't he?"

But after years of drug addiction and clashes with the law, the Marquess is a reformed character.

He has been drug-free for several years and moved back to Blenheim Palace following a rapprochement.

The Marquess's renewed relationship with his father was charted in a 2012 Channel 4 documentary called The Aristocrats.

At that point the late Duke said: "I am fully confident that James will be able to keep this place [Blenheim Palace] going. But over the top of him, and over the top of me, are trustees.

"You can't predict the future. You never know - God forbid - whether you would get behind the problems again but things are looking much more settled at the moment.

"Trying to keep Blenheim going is a very important part of the family's history and life at the present time, and so what we're trying to do is ensure that Blenheim is kept for future generations."

The Duke was vice president of the Conservative Association in the Witney, Oxfordshire constituency of David Cameron.

His full name was John George Vanderbilt Henry Spencer-Churchill and he had been married four times and has four surviving children.

There are two from his first marriage to Susan Hornby of the WH Smith Dynasty, and two from his third marriage to Rosita Spencer-Churchill.

His second marriage was childless and lasted 10 years, to Athina Onassis, the former wife of Aristotle Onassis.

In 2008 he married his fourth wife, Lily Sahni, the daughter of a successful Indian businessman, who was more than 30 years his junior.