Mohammed Al Fayed's lawyers dredged up 12th-century palace intrigue to argue why they wanted to summon Prince Philip to testify at the inquest into Princess Diana's death, three judges said in a written ruling published Thursday.

The lawyers alleged that British secret agents took it upon themselves to kill Diana after hearing that Prince Philip was angry at her, much like King Henry II's knights did when they assassinated the Archbishop of Canterbury more than 800 years ago.

The judges on March 18 rejected a late attempt by Al Fayed's lawyers to put written questions to Queen Elizabeth II and to put her husband Philip in the witness box.

Click here for photos of Princess Diana.

The inquest jury decided on Monday that Diana and Al Fayed's son, Dodi Fayed, were unlawfully killed by the reckless actions and drinking of their driver, Henri Paul, and the reckless actions of paparazzi photographers who chased the couple through Paris.

The ruling disclosed that Al Fayed's lawyers had acknowledged there was no evidence that the prince had directed what Al Fayed called a murder plot carried out by the Secret Intelligence Service against the couple.

But as the inquest was drawing to a close, Al Fayed's legal team suggested that the prince might have created a climate that encouraged others to act on their own.

"This suggestion ... was based on what was described as a troublesome or 'turbulent' priest thesis, a reference to the consequences of King Henry II's denigration of Thomas Becket, and the hasty rush in 1170 by four knights to murder him in Canterbury Cathedral," the judges said.

They dismissed it as a "newly minted speculative theory."

Al Fayed's lawyers had wanted to ask the queen about claims by Diana's former butler, Paul Burrell. He said that during a long meeting with the queen on Dec. 19, 1997, she had warned him: "Be careful, Paul. No one has been as close to a member of my family as you have. There are powers at work in this country about which we have no knowledge."

Becket, archbishop of Canterbury, stood up for the church in disagreements with the king. The four knights believed king wanted Becket out of the way, and killed him.

Sir Igor Judge and Justices Peter Gross and Paul Walker also upheld the decision by the coroner, Lord Justice Scott Baker, not to put written questions to Queen Elizabeth II.

When they heard arguments on March 18, the judges dismissed the appeal without waiting for any arguments against it.

The inquest also has released a transcript of the arguments on March 7.

When Al Fayed's lawyer Michael Mansfield raised the issue, Baker remarked that there were times when he thought he heard "the scraping of the bottom of the barrel."

"Many issues have been explored in the greatest of detail, but that does not mean that we go on forever exploring everything, whatever minute benefit there might be from it," Baker said.

Richard Horwell, a lawyer for London's Metropolitan Police, argued that there was no evidence linking the prince to the deaths — a point which Mansfield had conceded.

"There has been not one word of evidence to suggest that the Duke of Edinburgh ordered the princess to be harmed or ordered her to be intimidated," Horwell said.

"There is a vast chasm between possible frustration or irritation at certain of her actions and an intention to execute her. We submit that the proposition on the grounds advanced a preposterous, and remains so, after five months of the evidence being tested," Horwell said.