Despite an aristocratic pedigree—it’s about royalty, after all, and between them director Oliver Hirschbiegel and star Naomi Watts have rightly been nominated for lots of awards—“Diana” is rather tacky.

Not visually, of course: the locations are lovely, the interiors plush, and the costuming first-class all the way. Production designer Kave Quinn, art director Mark Raggett, set decorator Niamh Coulter and costume designer Julian Day have all done their jobs well, and their work has been set off attractively by cinematographer Rainer Klausmann.

Nor can one fault Watts. Though she doesn’t really resemble Diana very much, she gets the voice and mannerisms right in a turn that one might compare to Helena Bonham Carter’s as Liz Taylor in BBC America’s “Elizabeth and Richard.” Neither seems the best choice, but each does remarkably well under the circumstances.

No, the basic problem lies in the script, fashioned by Stephen Jeffreys from Kate Snell’s 2001 book “Diana: Her Last Love,” which depicts a two-year affair between the princess and Hasmat Khan, a Pakistani-British surgeon, which began in 1995 and ended shortly before her death in 1997. In this telling, Diana’s short involvement with Dodi Fayed was little more than a rather sordid attempt to make Khan jealous in order to overcome his reluctance to commit to marriage with her, largely because he couldn’t cope with the damage wedding such a very public person would do to his medical career (and to the privacy of his extended family back in Lahore).

Perhaps a trenchant story of a woman scorned by her husband who seeks romance elsewhere could be fashioned from this basic material, but Jeffreys has turned it into a “poor little rich girl” tale with Diana portrayed as a naïve, needy young woman hurt by estrangement from her husband, limited access to her children, William and Harry, and public criticism but buoyed by attention given to her charitable activities, especially her campaign to outlaw land mines. Her

Most of the attention is devoted, however, to her relationship with Khan (Naveen Andrews), whom she meets “cute” during a visit to his hospital to visit the ill husband of her confidante Oonah Shanley-Toffolo (Geraldine James). Soon they’re a secret item, with him sneaking into her residence for dinner and her donning a black wig to go out to a jazz club with him. Unfortunately, Andrews proves a stiff presence as the man the royal guards at the residence get very familiar with, and the dialogue Jeffreys provides for his scenes with Watts—presumably created out of whole cloth—Is so forced and banal that it sounds as though it had been written for a 1940s melodrama.

Though it sounds a bit cruel to say so, the film that “Diana” might remind you most of is Anthony Asquith’s 1960 adaptation of George Bernard Shaw’s “The Millionairess,” with Sophia Loren a wealthy but unhappy heiress romancing an Indian doctor, played by Peter Sellers with a thick accent. Of course, in that case the picture was intended to be a comedy. This one is likely, because of its heavy-handedness, to provoke snickers inadvertently.

A humorous song that Sellers and Loren recorded to promote their picture bears a title that could well represent a proper reaction to this one. It was “Goodness gracious me!”