Countess Raine Spencer, the stepmother of Diana, princess of Wales with whom she had a rocky relationship, has died aged 87, her family said.

The aristocrat died peacefully at her London home on Friday "after a short illness", her family announced in a brief statement.

The only child of the prolific romantic novelist Dame Barbara Cartland, she grew up and lived her life in the high society world of upper-class England.

Known for her bouffant hairstyle, pearls, immaculate dress sense and posh accent, she married three times in her life, amassing a collection of aristocratic titles.

She had four children with her first husband Gerald Legge, ninth earl of Dartmouth, whom she married in 1947.

She met Diana's father Earl John Spencer in the early 1970s and they married in 1976, when Diana was 15.

Diana, who married the heir to the throne Prince Charles in 1981, had a strained relationship with the countess.

Diana and her sisters nicknamed her "Acid Raine".

Majesty magazine editor Ingrid Seward, a friend of the countess, told the BBC: "When she first married Spencer, they loathed her. And they made her life extremely difficult.

"Raine was very stoic and she put up with it all."

She heavily redecorated the Spencer family seat at Althorp in Northamptonshire, central England, selling off many family treasures to do so.

However, there was a reported reconciliation with Diana in the early 1990s.

The countess was credited with nursing Diana's father back to health.

"I think Diana suddenly saw that this stepmother wasn't as bad as she had imagined," said Seward.

"And then later in Diana's life -- almost at the end of her life -- suddenly Raine Spencer was Diana's best friend."

The countess told the inquest into Diana's 1997 death in a Paris car crash: "She always said I had no hidden agenda. So many people, because she was so popular and so world famous, wanted something out of her. It was a very draining life."

And she told Gentlewoman magazine last year: "She had incredibly heavy pressures put upon her, but we ended up huge friends. She used to come and sit on my sofa and tell me her troubles."

She married Comte Jean-Francois Pineton de Chambrun in 1993 but her marriage to the French aristocrat lasted just two years.

One of her sons, William Legge, is the Earl of Dartmouth and a member of the European Parliament for the UK Independence Party.