After 2013's disastrous biopic Diana, starring Naomi Watts, it was something of a shock that filmmaker Olivier Dahan soldiered on to make Grace of Monaco, starring Watt's best pal Nicole Kidman. Reviews for both films were uniformly awful, so at least the actresses will have something to laugh about over dinner.

Nicole Kidman Grace of MonacoNicole Kidman [L] as Grace Kelly in 'Grace of Monaco'

The odd thing is that both Diana and Grace of Monaco were made by European filmmakers who have strong pedigrees. Diana was directed by German filmmaker Oliver Hirschbiegel, whose Downfall (2004) is considered one of the finest movies ever made about the collapse of Nazi rule. Meanwhile, Dahan directed Marion Cotillard to an Oscar in the Edith Piaf biopic La Vie en Rose (2007).

More: read our full review of 'Grace of Monaco' (if you have no intention of seeing it)

So what went wrong? The answer is fairly simple (and obvious): real-life princesses live notoriously protected lives. The people who knew Diana and Grace best would never dream of talking to a screenwriter, so both films are based on rumours and conjecture. Which leaves them feeling corny and melodramatic. Not to mention the impossibility of anyone adequately playing someone as iconic as either Princess Diana or Princess Grace.

No, to find a great movie about a princess, you really need to turn to Disney and the likes of Snow White, Sleeping Beauty, Cinderella and The Little Mermaid. And of course the two best screen princesses are Leia from Star Wars and Buttercup from The Princess Bride.

More: watch the 'Grace of Monaco' trailer - if you dare