A young, pre-queen Elizabeth (Sarah Gadon) and her sister Margaret (Bel Powley) share a princess’ night on the town in this frothy, forgettable comedy from director Julian Jarrold (“Kinky Boots”), which plays as a sort of footnote to 2010’s “The King’s Speech.” As King George VI (Rupert Everett) nervously prepares to address the nation on V-E Day in 1945, his cloistered daughters long to celebrate with the people.

And, in a plot based very loosely on real events, they do.

There’s more to it, but not much. Unless viewers are aficionados of the old royal family, I’m not sure how interested they’ll be in following two posh-accented young women chasing through drunken crowds in period dress, though Powley, in particular, is a charmer.

The cautious Elizabeth makes the acquaintance of a surly but gallant soldier (Jack Reynor), while adventurous Margaret swills Champagne on a (gasp!) public bus and chats with prostitutes. But too many wide, generic shots of celebrating Londoners drag this historical girls’ night down.