LONDON - Princess Diana's stepmother told an inquest on Wednesday she thought Diana and Dodi al-Fayed were "madly in love" and planning to wed before their deaths in a 1997 Paris road crash.

Countess Spencer, daughter of romantic novelist Barbara Cartland, ended an hour of testimony to the High Court by pleading with the judge, jury and lawyers to do their utmost to solve any mystery over the deaths.

Dodi's father Mohamed al-Fayed, owner of the Harrods luxury shop in London, alleges Diana and his son were killed by British security services on the orders of Prince Philip.

Fayed believes her killing was ordered because the royal family did not want the mother of the future king having a child with his son. He alleges Diana's body was embalmed to cover up evidence she was expecting a baby.

"Diana was madly in love with (Dodi)," said the countess, dressed in a black hat with a veil drawn back off her face.

"She said she had never been so happy for years. That was the moment I really felt it was highly likely that she and Dodi would get engaged and then get married."

Asked if Diana had ever mentioned being pregnant, the countess said: "Diana was brought up in a quite old-fashioned way. I don't personally believe she would have considered it."

She dismissed allegations of bad blood between Diana and Prince Philip.

"I do beg you to do your utmost to solve this mystery, to tear aside anything that could be a cover-up ... in order to allow poor Diana and poor Dodi to at last truly rest in peace," the countess told the court.

Diana and Dodi were killed in August 1997 when their limousine, driven by chauffeur Henri Paul, crashed at high speed in a Paris road tunnel.

Under English law, an inquest is needed to determine the cause of death when someone dies unnaturally.

The inquest, expected to last up to six months, was opened after major British and French police investigations.

They both concluded Diana and Dodi died because Paul was inebriated and driving too fast.

Diana was reconciled with her stepmother in the last years of her life. Relations had been frosty after the countess married her father.