Why does it take a 10-year investigation to determine that Britain’s storied Princess Diana died because a drunken driver was behind the wheel of the car in which she was riding?

Consider the waste of money and resources it took for an in-depth police inquiry that has ruled out numerous conspiracy theories in Diana’s death and concluded that an intoxicated driver was driving at a ridiculous speed to avoid photographers in pursuit.

Tests long ago determined that the blood alcohol level of the driver was about three times the legal limit. But the case was clouded by a conspiracy theory, pressed by the father of the man who was with Diana, and reports that the princess was pregnant.

The father of Dodi Fayed, who also died in the crash, continues to declare there was a conspiracy to have Diana and Dodi killed, perhaps to ease the opportunity for ex-husband Prince Charles to marry Camilla Parker Bowles sooner and with less fanfare. Yet the long-term probe indicates that Princess Diana was not intending to marry Dodi and was not carrying his child at the time of the violent death.

The crash occurred Aug. 31, 1997, in the Pont d’Alma tunnel in Paris. The driver, Dodi and Diana died and a bodyguard was badly hurt.

The father, Mohammed Fayed, owner of the famed Harrod’s department store in London, says the couple was killed in a conspiracy plotted by the British establishment, including Prince Philip, husband of Queen Elizabeth II, and British intelligence agencies. Supposedly they were opposed to a one-time member of the royal family marrying someone with an Islamic background.

Even though the probe determined Dodi and Diana were not due to wed, the father has taken the ring Dodi presumably had given Diana as a “promise” and put it on display, under a microscope, in a tacky, Egyptianized display in his department store. With such commercialization of the tragedy, little wonder he does not want the controversy to die down. Business is business!

How in the world can it take nearly 10 years to determine what happened in this case? The driver was drunk, paparazzi were poised to shoot pictures of Dodi and Diana, then gave chase when the car sped off.

The final finding: A drunken driving accident caused fatalities due to high speed, impairment and hard pursuit by photographers. To push it beyond that is ludicrous.

But Princess Diana long ago became a darling of romanticists inclined to engage in conspiracy theories, and they will never let facts spoil their beloved story about “star-crossed lovers.” And even if they fail, the elder Fayad is likely to continue his publicity-producing charade.